Hydraulic brake system

ABSTRACT

A mechanical pressurization device is connected to a common passage, and brake cylinders provided respectively for front left and right and rear left and right wheels are connected to the common passage respectively via pressure holding valves. Each of the pressure holding valves in the front is a normally open valve, and each of the pressure holding valves in the rear is a normally closed valve. In the event of an abnormality in which a hydraulic pressure in the common passage cannot be controlled using a hydraulic pressure produced by a power hydraulic pressure source, a hydraulic pressure in the mechanical pressurization device is supplied to the front brake cylinders provided respectively for the front left and right wheels.

TECHNICAL FIELD

The present invention relates to a hydraulic brake system including ahydraulic brake configured to restrain rotation of a wheel.

BACKGROUND ART

Patent Document 1 discloses a hydraulic brake system including (a) ahydraulic brake designed to restrain rotation of a wheel, (b) a mastercylinder, (c) an accumulator, (d) a pressurization mechanism utilizing ahydraulic pressure in the accumulator and activatable by activation ofan electric actuator, and (e) a selective valve designed to select ahigher one of a hydraulic pressure in the pressurization mechanism and ahydraulic pressure in the master cylinder to supply the selectedhydraulic pressure to a brake cylinder of the hydraulic brake.

Patent Document 2 discloses a hydraulic brake system including (a)hydraulic brakes provided for front right, front left, rear right andrear left wheels of a vehicle and designed to restrain rotations of thewheels, (b) a master cylinder, (c) a mechanical booster provided betweenthe master cylinder and brake cylinders of ones of the hydraulic brakeswhich are provided for the front right and front left wheels, (d) a highpressure source and an electromagnetic valve that is configured tocontrol a hydraulic pressure produced by the high pressure source.

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] JP-T-2009-502645

[Patent Document 2] JP-A-10-287227

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to improve a hydraulic brakesystem.

Means for Solving Problem and Effects

A hydraulic brake system according to the present invention isconfigured to, where a hydraulic pressure produced by a power hydraulicpressure source cannot be controlled, supply a servo pressure as anoutput hydraulic pressure provided by a pressurization device, to brakecylinders provided respectively for at least two wheels including frontleft and right wheels (i.e., front left and front right wheels).

Where the servo pressure is supplied to the brake cylinders providedrespectively for the at least two wheels including the front left andright wheels, it is possible to reduce a possibility of shortage of abraking force in an entire vehicle when compared with a case where amanual hydraulic pressure is supplied to the brake cylinders.

Forms of the Invention

There will be described by way of examples forms of inventionsrecognized to be claimable by the present applicant. The inventions maybe hereinafter referred to as “claimable inventions” and include atleast the inventions as defined in the appended claims. Nevertheless,the inventions may further include an invention of a concept subordinateor superordinate to the concept of the invention defined in the appendedclaims, and/or an invention of a concept different from the concept ofthe invention defined in the appended claims. The forms are numberedlike the appended claims. Features of the claimable inventions may beimplemented as features contained respectively in the following forms oras features contained respectively in combinations of two or more of thefollowing forms. Any one of the following forms may be implemented withone or more features added, or one or more of a plurality of featuresincluded in any one of the following forms are not necessarily providedall together.

(1) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for a plurality ofwheels of a vehicle and each configured to be operated by a hydraulicpressure in a corresponding one of a plurality of brake cylinders torestrain rotation of a corresponding one of the plurality of wheels;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device comprising a movable unit configured to beoperated by at least a hydraulic pressure produced by one manualhydraulic pressure source of the at least one manual hydraulic pressuresource, the pressurization device being capable of outputting ahydraulic pressure that is greater than the hydraulic pressure producedby the one manual hydraulic pressure source; and

a common passage to which the pressurization device is connected and towhich the plurality of brake cylinders are connected,

the hydraulic brake system further comprising:

at least one manual passage that bypasses the pressurization device andconnects between each of at least one of the at least one manualhydraulic pressure source and a corresponding one of at least one of theplurality of brake cylinders; and

a normally-closed manual cut-off valve provided in each of the at leastone manual passage.

The manual hydraulic pressure source may be a pressure chamber of themaster cylinder or a hydraulic booster. The hydraulic brake system mayinclude one manual hydraulic pressure source or two or more manualhydraulic pressure sources.

The hydraulic brake system may include, for example, two manualhydraulic pressure sources. Examples of this configuration include: acase where the hydraulic brake system includes a tandem master cylinderhaving two pressure chambers; and a case where the hydraulic brakesystem includes a hydraulic booster and a master cylinder having onepressure chamber. In addition, it is possible to consider that each ofthe manual hydraulic pressure sources also has a master reservoir. Thisis because the pressure chamber and the master reservoir are incommunication with each other in a case where a brake operating memberis not being operated. The hydraulic brake system may further include avacuum booster.

The at least one manual passage is configured to bypass thepressurization device to connect between each of the at least one of theat least one manual hydraulic pressure source and a corresponding one ofthe at least one of the plurality of brake cylinders.

For example, in the case where the hydraulic brake system includes twomanual hydraulic pressure sources, manual passages may be connected tothe respective two manual hydraulic pressure sources, and alternativelya manual passage may be connected to one of the two manual hydraulicpressure sources.

Also, one brake cylinder may be connected to one manual hydraulicpressure source via the manual passage, and at least two brake cylindersmay be connected to one manual hydraulic pressure source via the manualpassage(s).

Also, examples of a passage connecting between the manual hydraulicpressure source and at least one brake cylinder include a direct manualpassage (that bypasses the pressurization device) and an indirect manualpassage (that extends through the pressurization device). In thehydraulic brake system in the present form, there are (i) a case wheremanual passages (i.e., direct manual passages) are connected to therespective two manual hydraulic pressure sources and (ii) a case where adirect manual passage is connected to one of two manual hydraulicpressure sources, and an indirect manual passage is connected to theother of the two manual hydraulic pressure sources. Specifically, thereare: a case where both the direct manual passage and the indirect manualpassage are connected to the pressurization-device-coupled manualhydraulic pressure source, and a case where the indirect manual passageis connected to the pressurization-device-coupled manual hydraulicpressure source, and the direct manual passage is not connected to thepressurization-device-coupled manual hydraulic pressure source, forexample.

In any case, a normally closed manual cut-off valve is provided in eachof all the direct manual passages in the hydraulic brake system in thepresent form.

The manual cut-off valve is an electromagnetic open/close valvecontrollable to be placed in at least an open state and a closed state.The electromagnetic open/close valve may be either a linear controlvalve or a simple open/close valve. In the linear control valve, ahigh-low pressure differential (and/or an opening degree) of the valveis continuously controllable by continuously controlling an amount of acurrent supplied to a solenoid of the valve. In the simple open/closevalve, the open and closed states can be selectively established byselectively turning ON/OFF supply of a current to a solenoid of thevalve. In the following description, the term “valve” as used in anelectromagnetic open/close valve, an electromagnetic control valve, anda hydraulic-pressure control valve may be interpreted as either a linearcontrol valve or a simple open/close valve, unless otherwise specified.

(2) The hydraulic brake system may comprise: a power hydraulic pressuresource configured to produce a hydraulic pressure by supply of electricenergy; and a power hydraulic-pressure control device configured tocontrol a hydraulic pressure in the common passage by utilizing thehydraulic pressure produced by the power hydraulic pressure source.

While the power hydraulic pressure source comprises a pump deviceconfigured to produce the hydraulic pressure by the supply of theelectric energy, the power hydraulic pressure source may comprise anaccumulator configured to store working fluid ejected from the pumpdevice in a state in which the working fluid is pressurized. Even in acase where electric energy cannot be supplied to the power hydraulicpressure source, when a hydraulic pressure of the working fluidaccumulated in the accumulator is equal to or higher than a setpressure, high-pressure working fluid can be output.

The power hydraulic-pressure control device may comprise ahydraulic-pressure control valve provided between the power hydraulicpressure source and the common passage and configured to control thehydraulic-pressure control valve to control a hydraulic pressure to besupplied to the common passage (i.e., a power control pressure) (notedthat the power hydraulic-pressure control device may further comprise ahydraulic-pressure control valve provided between the common passage anda low pressure source). Also, the power hydraulic-pressure controldevice may be configured to control the power hydraulic pressure source(e.g., a pump motor) to control the hydraulic pressure to be supplied tothe common passage (i.e., the power control pressure), for example. Thehydraulic-pressure control valve provided between the common passage andthe power hydraulic pressure source can serve as apower-hydraulic-pressure-source cut-off valve configured to fluidicallycouple and decouple the power hydraulic pressure source to and from thecommon passage.

(3) The pressurization device may be configured to be capable ofoutputting a hydraulic pressure that is greater than the hydraulicpressure produced by the pressurization-device-coupled manual hydraulicpressure source, by utilizing the hydraulic pressure produced by thepower hydraulic pressure source.

It is noted that the movable unit may be configured to be operated byonly the hydraulic pressure produced by thepressurization-device-coupled manual hydraulic pressure source and maybe configured to be operated by both of the hydraulic pressure producedby the pressurization-device-coupled manual hydraulic pressure sourceand an electromagnetic driving force of a solenoid. In the latterconfiguration, the movable unit may be configured to control and outputthe hydraulic pressure produced by the power hydraulic pressure source,by control of a current to be supplied to the solenoid. For example, themovable unit may be configured to be capable of outputting a hydraulicpressure that is lower than a hydraulic pressure produced by a manualhydraulic pressure source included in the hydraulic brake system and maybe configured to be capable of outputting a hydraulic pressure even whenno hydraulic pressure is produced by the manual hydraulic pressuresource.

(4) The pressurization device may comprise anintra-pressurization-device communication passage capable of connectingthe pressurization-device-coupled manual hydraulic pressure source andthe common passage to each other, and the hydraulic brake system maycomprise an outflow preventing device configured to allow a flow of theworking fluid between the pressurization-device-coupled manual hydraulicpressure source and at least one of the plurality of brake cylindersthrough the intra-pressurization-device communication passage within atleast a period in the braking operation and prevent an outflow of theworking fluid from the pressurization-device-coupled manual hydraulicpressure source to the at least one brake cylinder through theintra-pressurization-device communication passage when the brakingoperation is not being performed.

The intra-pressurization-device communication passage is a passagecapable of connecting the pressurization-device-coupled manual hydraulicpressure source and the common passage to each other. The term “passagecapable of connecting” means a passage that allows a flow of the workingfluid between connected components. The intra-pressurization-devicecommunication passage may be a passage formed in the movable unit oroutside the movable unit (in this configuration, the passage bypassesthe movable unit).

In the hydraulic brake system in the present form, for example, when thebrake operating member is operated in such a direction that places thehydraulic brake in a working state (hereinafter may be referred to as“brake actuating operation”), the hydraulic pressure produced by thepressurization-device-coupled manual hydraulic pressure source may besupplied to the at least one brake cylinder via theintra-pressurization-device communication passage (i.e., a passagebypassing the movable unit) before the actuation of the movable unit ata start of the brake actuating operation (that is, before an actuatingpressure of the movable unit is reached). Also, when the brake operatingmember is operated in such a direction that places the hydraulic brakein a non-working state (hereinafter may be referred to as “brakereleasing operation”), the working fluid may be returned from the atleast one brake cylinder to the pressurization-device-coupled manualhydraulic pressure source via the intra-pressurization-devicecommunication passage.

Incidentally, in a case where the system is configured such that theservo pressure provided by the pressurization device is supplied to thecommon passage and then to the at least one brake cylinder of theplurality of brake cylinders in the event of an abnormality or failurein the control system, a normally-closed electromagnetic control valveis not usually provided in a passage passing through the pressurizationdevice and fluidically coupling the pressurization-device-coupled manualhydraulic pressure source with the at least one brake cylinder. Thus,when no current is supplied to a solenoid of the electromagnetic controlvalve, the pressurization-device-coupled manual hydraulic pressuresource and the at least one brake cylinder are in communication witheach other via the intra-pressurization-device communication passage.

In contrast, the present hydraulic brake system comprises the outflowpreventing device, and when the braking operation (noted that the term“braking operation” is used in a case where the brake actuatingoperation and the brake releasing operation do not need to bedistinguished or in a case where the braking operation can apply to boththe brake actuating operation and the brake releasing operation) is notbeing performed, a flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder via the intra-pressurization-devicecommunication passage is prevented. Thus, even in the event of fluidleakage in at least one of the at least one brake cylinder, it ispossible to prevent the outflow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source via theintra-pressurization-device communication passage.

It is noted that the abnormality in the control system is an abnormalityor failure in which the system cannot electrically control the hydraulicpressure in the brake cylinder (or the hydraulic pressure in the commonpassage) by utilizing the hydraulic pressure produced by the powerhydraulic pressure source. For example, the abnormality in the controlsystem include: an abnormality in at least one constituent element ofthe control system; an abnormality in which the high-pressure workingfluid cannot be supplied from the power hydraulic pressure source; anabnormality in which the power hydraulic pressure source cannot becontrolled; and an abnormality in which the electromagnetic controlvalve or other similar devices cannot be operated as commanded, and theabnormality in the control system may be one due to the abnormality inthe electrical system. In the event of the abnormality in the controlsystem, no current (i.e., electric power or electric energy) is suppliedto, e.g., solenoids of all the electromagnetic open/close valvescontained in the hydraulic brake system.

Also, the case where the braking operation is not being performed is acase where the brake operating member is located at its back endposition, i.e., a case where neither the brake actuating operation northe brake releasing operation is performed by the driver. The mainswitch may be an ON state or an OFF state.

Also, the number of intra-pressurization-device communication passagesmay be one or more. The number of intra-pressurization-devicecommunication passages means the number of communication passages formedindependently of one another and not intersecting one another though atleast one of a starting point and an end point may be the same.

Also, the “at least one of the plurality of brake cylinders” in thepresent form (referred to as “brake cylinder X” in the present form towhich an indirect manual passage is connected) may be the same as ordifferent from the “at least one of the plurality of brake cylinders” inthe preceding form (referred to as “brake cylinder Y” in the presentform to which a direct manual passage is connected). Also, the brakecylinders X and Y may be identical to each other only partly, and one ofthe brake cylinders X and Y may include the other.

For example, in a case where the hydraulic brake system includes twomanual hydraulic pressure sources, and (a) where direct manual passagesare connected to the respective two manual hydraulic pressure sources,and normally-closed manual cut-off valves are provided in the respectivetwo direct manual passages or (b) where an indirect manual passage isconnected to the pressurization-device-coupled manual hydraulic pressuresource, and the outflow preventing device is provided in the indirectmanual passage, it is possible to reliably prevent an outflow of theworking fluid from the two manual hydraulic pressure sources in the casewhere the braking operation is not being performed.

(5) The outflow preventing device may be provided for at least one of(a) a manual-hydraulic-pressure input passage configured to fluidicallycouple the pressurization device and the pressurization-device-coupledmanual hydraulic pressure source with each other, (b) theintra-pressurization-device communication passage, (c) a servo-pressurepassage configured to connect the pressurization device and the commonpassage to each other, (d) the common passage, and (e) at least onebrake-side passage configured to connect the common passage and the atleast one brake cylinder to each other.

For example, in a case where the pressurization-device-coupled manualhydraulic pressure source and the at least one brake cylinder arefluidically coupled with each other via a liquid passage (i.e., theindirect manual passage) including the intra-pressurization-devicecommunication passage, the outflow preventing device can be provided ina portion of the indirect manual passage. In particular, the outflowpreventing device can be provided in the intra-pressurization-devicecommunication passage, or in the indirect manual passage at a positionlocated downstream of the intra-pressurization-device communicationpassage.

It is noted that the brake-side passage may be a passage (may bereferred to as “individual brake-side passage” and “individual passage”)that connects the one brake cylinder and the common passage to eachother and may be a passage that connects the at least two brakecylinders and the common passage to each other.

(6) The outflow preventing device may comprise a first check valveconfigured to: inhibit a flow of the working fluid from the at least onebrake cylinder to the pressurization-device-coupled manual hydraulicpressure source through the intra-pressurization-device communicationpassage; inhibit the flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder through the intra-pressurization-devicecommunication passage when a subtraction value obtained by subtracting ahydraulic pressure in the at least one brake cylinder from the hydraulicpressure produced by the manual hydraulic pressure source is equal to orless than a set value; and allow the flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder through the intra-pressurization-devicecommunication passage when the subtraction value is greater than the setvalue.

An excessively high valve opening pressure of the first check valve isnot preferable because the excessively high valve opening pressure maycause a delay in actuation of the brake. An excessively low valveopening pressure of the first check valve is not preferable because theexcessively low valve opening pressure cannot inhibit an outflow of theworking fluid from the manual hydraulic pressure source due to a heightdifference. To solve these problems, the set value as the valve openingpressure is set at a value that is determined on the basis of ahydraulic pressure difference due to a height difference between thepressurization-device-coupled manual hydraulic pressure source and theat least one brake cylinder.

In the case where the braking operation is not being performed, themanual hydraulic pressure source does not produce a hydraulic pressure,the pressure chamber of the master cylinder is in communication with themaster reservoir, and the hydraulic pressure produced by the manualhydraulic pressure source is nearly an atmospheric pressure. Also, thehydraulic pressure in the brake cylinder is nearly the atmosphericpressure, but there is a hydraulic pressure difference due to a heightdifference between the manual hydraulic pressure source and the brakecylinder. Thus, in the configuration in which the set value is the valuedetermined on the basis of the hydraulic pressure difference due to theheight difference, even if there is a leakage of the working fluid inthe at least one brake cylinder in the case where the braking operationis not being performed, it is possible to reliably prevent the outflowof the working fluid from the pressurization-device-coupled manualhydraulic pressure source. The valve opening pressure may be equal to orless than the hydraulic pressure due to the height difference.

Also, when the brake actuating operation is performed, the manualhydraulic pressure can be supplied from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder through the intra-pressurization-devicecommunication passage, thereby speedily actuating the hydraulic brake.

(7) The first check valve may be a seating valve that comprises a valveelement and a valve seat and be provided in an orientation in which agravity acting on the valve element comprises a component that isopposed to the direction of the flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder.

No springs are provided for the first check valve in the present form.Also, the valve element is spherical in shape (the valve element can bereferred to as “ball”). Thus, a value obtained by subtracting ahydraulic pressure on a side nearer to the at least one brake cylinderfrom a hydraulic pressure on a side nearer to thepressurization-device-coupled manual hydraulic pressure source becomesgreater than a valve opening pressure (i.e., the component of thegravity acting on the valve element) in a state in which the valveelement is seated on the valve seat. The valve element is moved off thevalve seat, so that the first check valve becomes its open state. Also,when the flow of the working fluid from the at least one brake cylinderto the pressurization-device-coupled manual hydraulic pressure source isgenerated in the open state of the first check valve, and thus a suctionforce is generated, the valve element is seated on the valve seat andbecomes the closed state. The first check valve is preferably providedwith a valve element retaining mechanism for limiting movement of thevalve element.

In the first check valve in the present form, the component (i.e., acomponent in an axial direction of the first check valve) of the gravityacting on the valve element is set so as to correspond to the set value(i.e., the height-difference-based set value). That is, the component isset such that the weight of the ball, an orientation of the check valve(e.g., an inclination angle thereof with respect to a horizontal line,noted that this check valve may be parallel to a vertical line), and soon satisfy the above-described conditions.

(8) The first check valve may be a cup seal check valve and provided inan orientation in which a direction in which a seal member of the firstcheck valve is easily bent coincides with the direction of the flow ofthe working fluid from the pressurization-device-coupled manualhydraulic pressure source to the at least one brake cylinder.

The seal member is bent and switched to its open state by the flow ofthe working fluid from the pressurization-device-coupled manualhydraulic pressure source to the at least one brake cylinder. The sealmember is hard to be bent in an opposite direction, thereby preventingthe flow of the working fluid from the at least one brake cylinder tothe pressurization-device-coupled manual hydraulic pressure source.

A material, shape, size, and so on of the seal member are designed suchthat a force required to bend the seal member in the direction in whichthe seal member is easily bent (elastically deformed) is the set value(i.e., a height-difference-based set value).

(9) The first check valve may be a seating valve that includes a valveelement and a valve seat, and the valve element is seated on the valveseat by a magnetic force that may be the set value (i.e., theheight-difference-based set value).

At least one of the valve element and the valve seat is formed of aferromagnetic material.

(10) The first check valve may be a relief valve, and a spring may havean urging force set at the set value.

(11) The outflow preventing device may comprise a second check valveprovided parallel to the first check valve and configured to allow theflow of the working fluid from the at least one brake cylinder to thepressurization-device-coupled manual hydraulic pressure source andinhibit the flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder.

The flow of the working fluid from the pressurization-device-coupledmanual hydraulic pressure source to the at least one brake cylinder isinhibited in the case where the braking operation is not beingperformed.

When the brake actuating operation is performed, the flow of the workingfluid from the pressurization-device-coupled manual hydraulic pressuresource to the at least one brake cylinder is allowed, and when the brakereleasing operation is performed, the flow of the working fluid from theat least one brake cylinder to the pressurization-device-coupled manualhydraulic pressure source is allowed.

(12) The movable unit may comprise a piston operable by the hydraulicpressure produced by the pressurization-device-coupled manual hydraulicpressure source, and the pressurization device may comprise (a) amovable-unit bypass passage that bypasses the movable unit to connectbetween the pressurization-device-coupled manual hydraulic pressuresource and the common passage, (b) an input-side check valve provided inthe movable-unit bypass passage and configured to: inhibit a flow of theworking fluid from the common passage to thepressurization-device-coupled manual hydraulic pressure source; allowthe flow of the working fluid from the pressurization-device-coupledmanual hydraulic pressure source to the at least one brake cylinder whena subtraction value obtained by subtracting the hydraulic pressure inthe at least one brake cylinder from the hydraulic pressure produced bythe pressurization-device-coupled manual hydraulic pressure source isgreater than the set value; and inhibit the flow of the working fluidfrom the manual hydraulic pressure source to the at least one brakecylinder when the subtraction value is equal to or less than the setvalue.

The movable-unit bypass passage corresponds to theintra-pressurization-device communication passage, and the input-sidecheck valve is a constituent element of the outflow preventing device.The input-side check valve corresponds to the first check valve.

It is noted that the piston may be a stepped piston comprising: a largediameter portion to which the hydraulic pressure produced by thepressurization-device-coupled manual hydraulic pressure source isapplied; and a small diameter portion that is communicates with thecommon passage.

(13) The piston may be a stepped piston comprising a large diameterportion and a small diameter portion, and the movable unit may comprise(i) a housing in which the stepped piston is fluid-tightly and slidablyfitted, (ii) a larger-diameter-side chamber provided in a vicinity ofthe large diameter portion of the stepped piston and coupled with thepressurization-device-coupled manual hydraulic pressure source, (iii) asmaller-diameter-side chamber provided in a vicinity of the smalldiameter portion of the stepped piston and coupled with the at least onebrake cylinder, (iv) a high pressure chamber coupled with the powerhydraulic pressure source, (v) a high-pressure supply valve disposedbetween the high pressure chamber and the smaller-diameter-side chamberand switchable from a closed state to an open state by forward movementof the stepped piston, (vi) an intra-piston communication passageprovided in the stepped piston and configured to couple thelarger-diameter-side chamber and the smaller-diameter-side chamber witheach other, and (vii) an intra-piston check valve provided in theintra-piston communication passage and configured to allow a flow of theworking fluid from the smaller-diameter-side chamber to thelarger-diameter-side chamber and inhibit a flow of the working fluidfrom the larger-diameter-side chamber to the smaller-diameter-sidechamber.

The intra-piston communication passage corresponds to theintra-pressurization-device communication passage, and the intra-pistoncheck valve is a constituent element of the outflow preventing device.The intra-piston check valve corresponds to the second check valve.

The intra-piston communication passage provided in the stepped piston islocated at a position where the intra-piston communication passagefluidically couples the smaller-diameter-side chamber and thelarger-diameter-side chamber, in a state in which the stepped piston isspaced apart from the high-pressure supply valve. However, in theintra-piston communication passage is provided the intra-piston checkvalve configured to allow the flow of the working fluid from thesmaller-diameter-side chamber to the larger-diameter-side chamber andinhibit the flow of the working fluid from the larger-diameter-sidechamber to the smaller-diameter-side chamber. Thus, even in the state inwhich the stepped piston is spaced apart from the high-pressure supplyvalve, it is possible to inhibit the flow of the working fluid from thepressurization-device-coupled manual hydraulic pressure source to the atleast one brake cylinder. Also, in the state in which the stepped pistonis spaced apart from the high-pressure supply valve, a flow of theworking fluid from at least one brake cylinder to thepressurization-device-coupled manual hydraulic pressure source isallowed, which prevents brake drag.

(14) The pressurization device may comprise a high-pressure-side checkvalve provided between the high pressure chamber and the power hydraulicpressure source and configured to allow a flow of the working fluid fromthe power hydraulic pressure source to the high pressure chamber andinhibit a flow of the working fluid from the high pressure chamber tothe power hydraulic pressure source.

In a configuration in which the high-pressure-side check valve isprovided, for example, even when a problem such as the abnormality inthe electrical system causes the electric energy not to be supplied tothe power hydraulic pressure source, and accordingly an output hydraulicpressure produced by the power hydraulic pressure source is lowered, itis possible to prevent a low hydraulic pressure from being supplied fromthe power hydraulic pressure source to the smaller-diameter-sidechamber, which can prevent lowering of the hydraulic pressure in thesmaller-diameter-side chamber.

(15) The hydraulic brake system may further comprise a normally-openoutput-side cut-off valve provided between the pressurization device andthe common passage.

In a case where the system works normally, the output-side cut-off valveis in a closed state, so that the pressurization device is isolated fromthe common passage. The power hydraulic-pressure control device controlsthe hydraulic pressure in the common passage by utilizing the hydraulicpressure produced by the power hydraulic pressure source.

In a case of an abnormality in the control system, for example, theoutput-side cut-off valve is in an open state, so that thepressurization device is in communication with the common passage. Aservo pressure provided by the pressurization device is supplied to theat least one brake cylinder via the common passage.

Since the output-side cut-off valve is the normally-open electromagneticopen/close valve, the output-side cut-off valve is in the open state inthe event of the abnormality in the control system.

(16) The hydraulic brake system may further comprise an operationcontrol valve switchable between a state in which the operation controlvalve allows an operation of the movable unit and a state in which theoperation control valve inhibits the operation of the movable unit.

For example, the operation control valve may be provided between thehigh pressure chamber of the movable unit and the power hydraulicpressure source (a high-pressure cut-off valve), may be provided betweenthe larger-diameter-side chamber and the pressurization-device-coupledmanual hydraulic pressure source (a movable-unit input-side cut-offvalve), may be provided between the smaller-diameter-side chamber andthe common passage (a movable-unit output-side cut-off valve), and maybe provided between the reservoir and a ring-shaped chamber providedbetween the stepped piston and the housing (a reservoir cut-off valve).When transfer and receipt of the working fluid are inhibited, theoperation of the movable unit (i.e., an operation causing a pressurizingoperation of the pressurization device) is inhibited, resulting in thatthe movable unit is not movable.

The operation control valve is preferably configured to establish thestate allowing the operation (i.e., the open state) in a case where nocurrent is supplied to a solenoid of the valve.

Also, the operation of the pressurization device is not always inhibitedby inhibiting the operation of the movable unit.

(17) The hydraulic brake system further comprises: an input-side cut-offvalve provided between the pressurization device and thepressurization-device-coupled manual hydraulic pressure source; and ahigh-pressure cut-off valve provided between the pressurization deviceand the power hydraulic pressure source.

When the high-pressure cut-off valve is switched to its closed state,the actuation of the movable unit can be suppressed. Also, when theinput-side cut-off valve is switched to its closed state, a flow of theworking fluid between the pressurization device and thepressurization-device-coupled manual hydraulic pressure source can beinhibited. Thus, the pressurization device can be kept in anon-operating state without providing the output-side cut-off valvebetween the pressurization device and the common passage, whereby thehydraulic pressure in the common passage can be controlled at ahydraulic pressure that is higher than that of thepressurization-device-coupled manual hydraulic pressure source. That is,the pressurization device can be directly connected to the commonpassage (without the electromagnetic open/close valve therebetween).

(18) The hydraulic brake system may further comprise a separate valveprovided in the common passage between (i) positions where the commonpassage is connected to brake-side passages for the brake cylindersprovided for the respective front left and right wheels and (ii)positions where the common passage is connected to brake-side passagesfor the brake cylinders provided for the respective rear left and rightwheels.

The separate valve can separate a brake line including the brakecylinders provided for the respective front left and right wheels and abrake line including the brake cylinders provided for the respectiverear left and right wheels from each other on a brake-cylinder side in astate in which the hydraulic pressure is supplied to the brake cylindersprovided for the respective four wheels.

Also, the above-described high-pressure-side cut-off valve can separatea line including the brake cylinders operated by the pressurizationdevice and a line including the brake cylinders operated by thehydraulic pressure produced by the power hydraulic pressure source fromeach other on a high-pressure side.

It is noted that the separate valve is not essential.

(19) The pressurization device is connected to the common passage, andan individual control valve corresponding to a brake cylinder that iscoupled to the separate valve on an opposite side of the separate valvefrom a position at which the pressurization device is coupled to theseparate valve is a normally open valve.

In the event of the abnormality in the control system, the working fluidis never supplied to the brake cylinders coupled to the separate valveon an opposite side of the separate valve from the pressurizationdevice. Thus, each of the individual control valves providedrespectively for these brake cylinders may be a normally-openelectromagnetic open/close valve. Each of a pressure holding valveprovided between the brake cylinder and the common passage and apressure reduction valve provided between the brake cylinder and thereservoir may also be a normally-open electromagnetic open/close valve.

(20) The hydraulic brakes are provided respectively for the front leftand right and rear left and right wheels of the vehicle, and thehydraulic brake system further comprises an abnormal-case servo-pressuresupply device configured to supply a servo pressure to at least twobrake cylinders of the plurality of brake cylinders in the event of theabnormality in the control system, wherein the servo pressure is anoutput hydraulic pressure provided by the pressurization device.

The abnormal-case servo-pressure supply device may be configured to oneof: (i) supply the servo pressure to the brake cylinders provided forthe respective front left and right wheels; (ii) supply the servopressure to brake cylinders provided respectively for two wheels locatedat a pair of diagonal positions; (iii) supply the servo pressure to thebrake cylinders provided for the respective front left and right wheelsand a brake cylinder provided for one of the rear left and right wheels;(iv) supply the servo pressure to brake cylinders provided respectivelyfor two wheels located at one pair of diagonal positions and a brakecylinder provided for one of two wheels located at the other pair ofdiagonal positions; and (v) supply the servo pressure to the brakecylinders provided respectively for the front left and right and rearleft and right wheels.

The number, positions, and so on of brake cylinders to receive the servopressure provided by the pressurization device in the event of theabnormality in the control system are determined by capabilities of thepressurization device (and capabilities of the manual hydraulic pressuresource in some cases), a state of the vehicle, and other conditions.

For example, in a case where the servo pressure is supplied to the brakecylinders provided respectively for two or three wheels such that abraking force applied to the left wheel(s) and a braking force appliedto the right wheel(s) differ from each other and in a case where acenter of gravity of the vehicle is not located at a center of thevehicle in a right and left direction, wheels (i.e., positions thereof)to which the servo pressure is to be supplied can be determined so as tosuppress generation of a yaw moment. Also, wheels (i.e., positionsthereof) to which the servo pressure is to be supplied can be determinedso as to generate a yaw moment in a direction that is desirable in termsof safety of driving. For example, in a region where legal regulationsstipulate that a vehicle having a driver's seat provided in its rightportion in a forward direction (namely, right-hand drive vehicle) mustrun on the left side of the road, wheels to which the servo pressure isto be supplied can be determined such that a yaw moment in aleft-turning direction is applied to the vehicle, and in a region wherelegal regulations stipulate that a vehicle having a driver's seatprovided in its left portion in the forward direction (namely, left-handdrive vehicle) must run on the right side of the road, wheels to whichthe servo pressure is to be supplied can be determined such that a yawmoment in a right-turning direction is applied to the vehicle.

It is noted that, in a case where the hydraulic brake system includestwo manual hydraulic pressure sources, one of which is not connected tothe pressurization device and the other of which is connected to thepressurization device, the volume (corresponding to an amount of workingfluid that can be supplied) of the pressurization-device-connectedmanual hydraulic pressure source can be larger than that of the othermanual hydraulic pressure source. This larger volume of thepressurization-device-connected manual hydraulic pressure source allowsan increase in the number of brake cylinders to which the servo pressurecan be supplied from the pressurization device in the event of theabnormality in the control system.

(21) The hydraulic brakes are provided respectively for the front leftand right and rear left and right wheels of the vehicle, at least two ofthe plurality of brake cylinders are connected to the common passagerespectively via brake-side passages in which a normally-openelectromagnetic open/close valve is provided.

In a case where each of the brake-side passages is the individualbrake-side passage for coupling a corresponding one of the brakecylinders and the common passage with each other, and the individualcontrol valves are provided in the respective individual brake-sidepassages, an individual control valve corresponding to a brake cylinderto which the servo pressure is to be supplied in the event of theabnormality in the control system as described above is a normally-openelectromagnetic open/close valve.

(22) Each of the at least one manual hydraulic pressure source may beconnected to the at least one manual passage.

(23) The at least one manual passage may be connected to at least one ofthe at least one manual hydraulic pressure source except thepressurization-device-coupled manual hydraulic pressure source.

(24) A normally-open electromagnetic open/close valve may be provided inat least one of the brake-side passages for coupling the common passageand at least one of the plurality of brake cylinders to which the atleast one manual passage is coupled.

(25) The hydraulic brake system comprises a supply-state control deviceconfigured to control states of respective hydraulic pressures suppliedto the plurality of respective brake cylinders.

(26) The supply-state control device comprises at least one of: (a) apower control pressure supplier configured to, when the powerhydraulic-pressure control device is in a state in which the powerhydraulic-pressure control device is capable of controlling thehydraulic pressure in the common passage, supply a power controlpressure to the plurality of brake cylinders, wherein the power controlpressure is a hydraulic pressure controlled by the powerhydraulic-pressure control device; (b) an abnormal-case servo pressuresupplier configured to, when the power hydraulic-pressure control devicecannot control the hydraulic pressure in the common passage, supply aservo pressure that is an output hydraulic pressure provided by thepressurization device, to at least two brake cylinders comprising thebrake cylinders provided for the respective front left and right wheelsof the plurality of brake cylinders; (c) a power-control-pressure andmanual-hydraulic-pressure supplier configured to, in case of possiblefluid leakage in the hydraulic brake system, supply the power controlpressure to the brake cylinders provided for the respective rear leftand right wheels and supply the manual hydraulic pressure to the brakecylinders provided for the respective front left and right wheels, and(d) a front-left-and-right-wheel manual hydraulic pressure supplierconfigured to, when a hydraulic pressure outputtable by the powerhydraulic pressure source is equal to or less than a set pressure,supply the manual hydraulic pressure to the brake cylinders provided forthe respective front left and right wheels.

(27) The hydraulic brake system further comprises at least onebrake-cylinder cut-off valve configured to disconnect the brakecylinders provided for the respective front left and right wheels fromthe common passage in a state in which the hydraulic pressure issupplied to the plurality of brake cylinders by thepower-control-pressure and manual-hydraulic-pressure supplier.

In the case where the hydraulic brake system works normally, the brakecylinders provided for the respective front left and right wheels areisolated from the manual hydraulic pressure sources, and the servopressure provided by the pressurization device is not supplied to thecommon passage (where the operation of the pressurization device isinhibited, the pressurization device may be disconnected from the commonpassage). The power control pressure is supplied to the brake cylindersprovided for the respective four wheels.

In the event of an abnormality in a control system of the hydraulicbrake system, the power hydraulic pressure source is isolated from thecommon passage, the manual hydraulic pressure sources are isolated fromthe brake cylinders provided for the respective front left and rightwheels, the operation of the pressurization device is allowed, and thepressurization device is connected to the common passage. The servopressure is applied to the brake cylinders that are in communicationwith the common passage.

In case of possible fluid leakage, the brake cylinders provided for therespective front left and right wheels are isolated from the commonpassage and coupled with the manual hydraulic pressure sources.Specifically, the brake cylinders provided for the respective front leftand right wheels are respectively coupled with the manual hydraulicpressure sources. The operation of the pressurization device isinhibited, and the brake cylinders provided for the respective rear leftand right wheels are connected to the common passage. Three lines aremade independent of one another, so that the power control pressure issupplied to the brake cylinders provided for the respective rear leftand right wheels, and the manual hydraulic pressures are respectivelysupplied to the brake cylinders provided for the respective front leftand right wheels.

Even in a case where the pressurization device cannot perform enoughpressure increase because the hydraulic pressure outputtable by thepower hydraulic pressure source is lower than the set pressure, apower-control-pressure and manual-hydraulic-pressure supply state can beestablished. In this case, the brake cylinders provided for therespective front left and right wheels are respectively coupled with themanual hydraulic pressure sources, resulting in lower possibility ofshortage of the hydraulic pressure. It is noted that the powerhydraulic-pressure control device may be configured not to be controlledin a case where hydraulic pressures in the brake cylinders provided forthe respective rear left and right wheels cannot be effectivelycontrolled because the output hydraulic pressure produced by the powerhydraulic pressure source is lower than the set pressure. This state maybe referred to as “front-left-and-right-wheel manual hydraulic pressuresupply state”.

It is noted that the above-described individual control valves may bebrake cut-off valves.

(28) The hydraulic brake system further comprises a brake circuitconfigured to, when a main switch of the vehicle is an OFF state,establish a state in which the brake cylinders provided for therespective front left and right wheels are decoupled from the manualhydraulic pressure source and connected to the common passage, thepressurization device is coupled and connected to the manual hydraulicpressure source and the common passage, the brake cylinders provided forthe respective rear left and right wheels are disconnected to the commonpassage, and the power hydraulic pressure source is disconnected fromthe common passage.

As described above, when the hydraulic pressure outputtable by the powerhydraulic pressure source is lower than the set pressure, the state inthe present form can be established.

(29) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for a plurality ofwheels of a vehicle and each configured to be operated by a hydraulicpressure in a corresponding one of a plurality of brake cylinders torestrain rotation of a corresponding one of the plurality of wheels;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver; and

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe at least one manual hydraulic pressure source, the pressurizationdevice being capable of outputting a hydraulic pressure that is greaterthan the hydraulic pressure produced by the one manual hydraulicpressure source,

the pressurization device comprising an intra-pressurization-devicecommunication passage capable of fluidically coupling apressurization-device-coupled manual hydraulic pressure source as theone manual hydraulic pressure source and at least one of the pluralityof brake cylinders with each other, the hydraulic brake system furthercomprising an outflow preventing device configured to allow a flow ofthe working fluid between the pressurization-device-coupled manualhydraulic pressure source and the at least one brake cylinder within atleast a period in the braking operation and prevent an outflow of theworking fluid from the pressurization-device-coupled manual hydraulicpressure source to the at least one brake cylinder when the brakingoperation is not being performed.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (27).

(30) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for a plurality ofwheels of a vehicle and each configured to be operated by a hydraulicpressure in a corresponding one of a plurality of brake cylinders torestrain rotation of a corresponding one of the plurality of wheels;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe at least one manual hydraulic pressure source, the pressurizationdevice being capable of outputting a hydraulic pressure that is greaterthan the hydraulic pressure produced by the one manual hydraulicpressure source;

a common passage to which the pressurization device and the plurality ofbrake cylinders are connected; and

a power hydraulic device comprising a power hydraulic pressure sourceconfigured to produce a hydraulic pressure by supply of electric energy,the power hydraulic device being capable of utilizing the hydraulicpressure produced by the power hydraulic pressure source to control ahydraulic pressure in the common passage,

the hydraulic brake system further comprising an outflow preventingdevice configured to prevent an outflow of the working fluid from theone manual hydraulic pressure source in a case where no electric energyis supplied to the hydraulic brake system, and the braking operation isnot being performed.

For example, the outflow preventing device may be configured to preventthe outflow of the working fluid from the one manual hydraulic pressuresource in a case where the main switch of the vehicle is in an OFFstate, and the braking operation is not being performed.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (28).

(31) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a hydraulic-pressure producing device configured to produce a hydraulicpressure;

a low pressure source;

a plurality of pressurization-side individual control valves providedbetween the plurality of respective brake cylinders and thehydraulic-pressure producing device; and

a plurality of pressure-reduction-side individual control valvesprovided between the plurality of respective brake cylinders and the lowpressure source,

wherein each of both of the plurality of pressurization-side individualcontrol valves and the plurality of pressure-reduction-side individualcontrol valves is a normally-open electromagnetic open/close valve.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (30). It is noted that eachof the plurality of pressurization-side individual control valve can bereferred to as “pressure holding valve”, and each of the plurality ofpressure-reduction-side individual control valves as “pressure reductionvalve”.

(32) The hydraulic brake system may further comprise a manual hydraulicpressure source configured to produce a hydraulic pressure by anoperation of a driver,

wherein the hydraulic-pressure producing device comprises at least apressurization device configured to be operated by the hydraulicpressure produced by the manual hydraulic pressure source,

wherein the hydraulic brake system further comprises (a) a commonpassage to which the plurality of brake cylinders are connected and towhich the pressurization device is connected and (b) a separate valvethat is a normally-closed electromagnetic open/close valve provided inthe common passage, and

wherein the plurality of pressurization-side individual control valvesare provided between the common passage and ones of the plurality ofbrake cylinders which are coupled to the common passage on an oppositeside of the separate valve from a position where the pressurizationdevice is coupled to the common passage, and the plurality ofpressure-reduction-side individual control valves are provided betweenthe low pressure source and the ones of the plurality of brakecylinders.

In the event of an abnormality in the control system, the working fluidis never supplied to the brake cylinders that are coupled to the commonpassage on an opposite side of the separate valve from a position wherethe pressurization device is coupled to the common passage. Thus, eachof the plurality of pressure-reduction-side individual control valvesmay be a normally open valve. Also, the plurality ofpressure-reduction-side individual control valves as the normally openvalves can prevent brake drag upon brake releasing. On the other hand,upon application of the hydraulic brake, the pressurization-sideindividual control valves are usually in open states. Thus, where theplurality of pressurization-side individual control valves are providedas normally-open electromagnetic open/close valves, power consumptioncan be reduced accordingly.

As described above, where each of both of the plurality ofpressurization-side individual control valves and the plurality ofpressure-reduction-side individual control valves is provided as anormally-open electromagnetic open/close valve, it is possible to reducethe power consumption upon brake application and prevent the brake dragupon brake releasing when compared with a case where each of thepressurization-side individual control valves is a normally-closedelectromagnetic open/close valve.

(33) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a power hydraulic pressure source configured to produce a hydraulicpressure by supply of electric energy;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe at least one manual hydraulic pressure source, the pressurizationdevice being capable of outputting a hydraulic pressure that is greaterthan the hydraulic pressure produced by the one manual hydraulicpressure source;

a common passage to which the pressurization device and the powerhydraulic pressure source are connected and to which the plurality ofbrake cylinders are connected;

a power hydraulic-pressure control device configured to control ahydraulic pressure in the common passage by utilizing the hydraulicpressure produced by the power hydraulic pressure source; and

an abnormal-case servo-pressure supply device configured to, when thepower hydraulic-pressure control device cannot control the hydraulicpressure in the common passage, supply a servo pressure to brakecylinders provided respectively for at least two wheels comprising frontleft and right wheels of the four wheels, wherein the servo pressure isan output hydraulic pressure provided by the pressurization device.

Where the servo pressure is supplied to the brake cylinders providedrespectively for the at least two wheels including the front left andright wheels, a large braking force can be applied to the entire vehiclewhen compared with a configuration in which a manual hydraulic pressureis supplied to the cylinders.

Also, in a case where the servo pressure is supplied to the brakecylinders provided for the respective front left and right wheels in theevent of an abnormality in which the power hydraulic-pressure controldevice cannot control the hydraulic pressure in the common passage andwhere the center of gravity of the entire vehicle is located atgenerally a center of the vehicle in the right and left direction, thegeneration of the yaw moment can be suppressed in the event of theabnormality.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (29).

It is noted that, while the plurality of brake cylinders are connectedto the common passage, the plurality of brake cylinders may be connectedto the common passage by the respective individual brake-side passagesor may be connected to the common passage such that at least two of thebrake cylinders are connected to the common passage in common by thebrake-side passage.

(34) The abnormal-case servo-pressure supply device may comprise athree-wheel supplier configured to supply the servo pressure to brakecylinders provided respectively for three wheels comprising the frontleft and right wheels.

For example, the servo pressure may be supplied to brake cylindersprovided respectively for the front left and right wheels and one of therear left and right wheels.

(35) The abnormal-case servo-pressure supply device may comprise afour-wheel supplier configured to supply the servo pressure to the brakecylinders provided respectively for the front left and right and rearleft and right wheels.

(36) The pressurization device comprises (a) anouter-circumferential-side cylindrical portion and aninner-circumferential-side cylindrical portion arranged one insideanother; and (b) a hydraulic-pressure control valve configured to coupleand decouple an output port connected to the common passage and a highpressure port coupled to the power hydraulic pressure source to and fromeach other by relative movement of the outer-circumferential-sidecylindrical portion and the inner-circumferential-side cylindricalportion in an axial direction thereof,

one of the outer-circumferential-side cylindrical portion and theinner-circumferential-side cylindrical portion is movable in the axialdirection by a hydraulic pressure produced by apressurization-device-coupled manual hydraulic pressure source as theone manual hydraulic pressure source, and another of theouter-circumferential-side cylindrical portion and theinner-circumferential-side cylindrical portion is movable by a motiveforce a solenoid.

A portion of the pressurization device which is operable by the motiveforce of the solenoid can be considered as a constituent element of thepower hydraulic-pressure control device.

The pressurization device is operable also by the motive force of thesolenoid, and a current to be supplied to the solenoid is controlled tocontrol a hydraulic pressure in the output port. The hydraulic pressurein the output port may be controlled to be lower than the hydraulicpressure produced by the manual hydraulic pressure source. Thus, thepressurization device in the present form can be referred to as“mechanical/power hydraulic-pressure control device having apressurization-device function”.

It is noted that in the event of an abnormality in which a currentcannot be supplied to the solenoid, the pressurization device can beoperated by the hydraulic pressure produced by the manual hydraulicpressure source to produce a hydraulic pressure that is higher than thehydraulic pressure produced by the manual hydraulic pressure source.Also, the inner-circumferential-side cylindrical portion may be any of asolid cylindrical portion and a hollow cylindrical portion.

(37) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe at least one manual hydraulic pressure source, the pressurizationdevice being capable of outputting a hydraulic pressure that is greaterthan the hydraulic pressure produced by the one manual hydraulicpressure source;

a common passage to which the pressurization device is connected and towhich the four brake cylinders are connected respectively via fourindividual brake-side passages; and

four individual control valves provided respectively in the fourindividual brake-side passages,

wherein each of individual control valves respectively provided for atleast two brake cylinders comprising the brake cylinders provided forthe respective front left and right wheels among the four individualcontrol valves is a normally open valve.

Where the pressurization device is connected to the common passage, andthe brake cylinders provided for the respective front left and rightwheels are connected to the common passage respectively via the normallyopen valves, the servo pressure provided by the pressurization devicecan be supplied to the brake cylinders provided for the respective frontleft and right wheels in the event of the abnormality in the electricalsystem.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (29).

(38) At least one of individual control valves provided corresponding tothe brake cylinders provided for the respective rear left and rightwheels among the four individual control valves is a normally closedvalve.

(39) Each of all the four individual control valves is a normally openvalve.

(40) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a power hydraulic pressure source configured to produce a hydraulicpressure by supply of electric energy;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe at least one manual hydraulic pressure source, the pressurizationdevice being capable of outputting a hydraulic pressure that is greaterthan the hydraulic pressure produced by the one manual hydraulicpressure source;

a common passage to which the pressurization device is connected and towhich the four brake cylinders are connected;

a power hydraulic-pressure control device capable of electricallycontrolling hydraulic pressures in the four brake cylinders by utilizingthe hydraulic pressure produced by the power hydraulic pressure source;and

an abnormal-case mechanical-pressure supply device capable of supplyingthe output hydraulic pressure provided by the pressurization device, atleast to at least two brake cylinders comprising the brake cylindersprovided for the respective front left and right wheels, when the powerhydraulic-pressure control device cannot control a hydraulic pressure inat least one of the four brake cylinders.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (36).

(41) A hydraulic brake system comprising:

a brake operating member provided in a vehicle and operable by a driver;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by an operation for the brake operating member;

a pressurization device configured to be operated by at least ahydraulic pressure produced by one manual hydraulic pressure source ofthe

at least one manual hydraulic pressure source, the pressurization devicebeing capable of outputting a hydraulic pressure that is greater thanthe hydraulic pressure produced by the one manual hydraulic pressuresource; and

an input-side cut-off valve that is an electromagnetic open/close valveprovided between the pressurization device and the one manual hydraulicpressure source.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (37).

(42) The hydraulic brake system may further comprise: a plurality ofhydraulic brakes provided respectively for a plurality of wheelsprovided on the vehicle and each configured to be operated by ahydraulic pressure in a corresponding one of a plurality of brakecylinders to restrain rotation of a corresponding one of the pluralityof wheels; and two manual hydraulic pressure sources each as the manualhydraulic pressure source,

wherein one of the two manual hydraulic pressure sources bypasses thepressurization device to be coupled to a first brake cylinder as atleast one of the plurality of brake cylinders via a first manualpassage,

wherein another of the two manual hydraulic pressure sources is coupledto a second brake cylinder as at least one of the plurality of brakecylinders via the pressurization device, and

wherein the input-side cut-off valve is a normally open valve providedbetween said another of the two manual hydraulic pressure sources andthe pressurization device.

In the hydraulic brake system in the present form, said another of thetwo manual hydraulic pressure sources corresponds to the one manualhydraulic pressure source.

Each of the first brake cylinder and the second brake cylinder may beconstituted by one cylinder or two or more cylinders. Also, the firstbrake cylinder and the second brake cylinder may be identical to eachother, differ from each other, partly identical to each other, or have arelationship in which one of the first brake cylinder and the secondbrake cylinder includes the other.

For example, the first brake cylinder may be a brake cylinder providedfor one of the front left and right wheels, and the second brakecylinder may include two brake cylinders provided respectively for thefront left and right wheels.

(43) The hydraulic brake system may further comprise:

a stroke simulator coupled to said another of the two manual hydraulicpressure sources; and

a first input-side cut-off valve control device configured to: place theinput-side cut-off valve in a closed state when the stroke simulator isallowed to be operated; and place the input-side cut-off valve in anopen state when the stroke simulator is inhibited from being operated.

(44) The hydraulic brake system may further comprise:

a plurality of hydraulic brakes provided respectively for a plurality ofwheels of the vehicle and each configured to be operated by a hydraulicpressure in a corresponding one of a plurality of brake cylinders torestrain rotation of a corresponding one of the plurality of wheels;

a power hydraulic pressure source configured to produce a hydraulicpressure by supply of electric energy;

a power hydraulic-pressure control device capable of utilizing thehydraulic pressure produced by the power hydraulic pressure source toelectrically control the hydraulic pressures in the plurality ofrespective brake cylinders; and

a second input-side cut-off valve control device configured to place theinput-side cut-off valve in the closed state when the powerhydraulic-pressure control device is in a normal state in which thepower hydraulic-pressure control device is capable of controlling thehydraulic pressures in the plurality of respective brake cylinders.

It is noted that the input-side cut-off valve can also be configured tobe placed in the closed state when the braking operation is performed,with the power hydraulic-pressure control device being in the normalstate.

(45) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the plurality of brakecylinders provided respectively for the front left and right and rearleft and right wheels; and

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to brake cylindersprovided respectively for three wheels of the four wheels.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (41).

(46) The manual hydraulic system may comprise: (a) two first manualhydraulic pressure sources each configured to produce a hydraulicpressure that is related to an operating force of a driver for a brakeoperating member; (b) a second manual hydraulic pressure source operableby a hydraulic pressure produced by one of the two first manualhydraulic pressure sources and configured to produce a hydraulicpressure that is greater than the hydraulic pressure produced by the oneof the two first manual hydraulic pressure sources; and (c) a mixed-typehydraulic pressure distributor capable of supplying a hydraulic pressureproduced by another of the two first manual hydraulic pressure sourcesto one or ones of the brake cylinders provided respectively for threewheels and supplying the hydraulic pressure produced by the secondmanual hydraulic pressure source to the other of the brake cylindersprovided respectively for three wheels.

For example, the system may be configured such that the first manualhydraulic pressure source is a tandem master cylinder, and the secondmanual hydraulic pressure source is a pressurization device.

In a case where the hydraulic pressure produced by the other of the twofirst manual hydraulic pressure sources is supplied to one or two of thethree brake cylinders, and the hydraulic pressure produced by the secondmanual hydraulic pressure source is supplied to remaining two or one ofthe brake cylinders, for example, in a case where the hydraulic pressureproduced by the other of the two first manual hydraulic pressure sourcesis supplied to the brake cylinder provided for one of the front left andright wheels, e.g., the front left wheel, the hydraulic pressureproduced by the second manual hydraulic pressure source is supplied tothe brake cylinder provided for the other of the front left and rightwheels, e.g., the front right wheel (that is, a braking force F_(FR)applied to the front right wheel is larger than a braking force F_(FL)applied to the front left wheel (F_(FR)>F_(FL))), and the hydraulicpressure produced by the second manual hydraulic pressure source issupplied to the brake cylinder provided for the rear left wheel, the sumof braking forces applied to left wheels is generally equal to the sumof braking forces applied to right wheels (F_(FR)+0≈F_(FL)+F_(RL)).

Thus, the system may be configured such that the hydraulic pressureproduced by the second manual hydraulic pressure source is supplied tothe diagonal wheels, and the hydraulic pressure produced by the firstmanual hydraulic pressure source is supplied to the other wheel.

(47) The manual hydraulic system may comprise: (a) at least one firstmanual hydraulic pressure source each configured to a hydraulic pressurethat is related to an operating force of a driver for a brake operatingmember; (b) a second manual hydraulic pressure source operable by ahydraulic pressure produced by one of the at least one first manualhydraulic pressure source and configured to produce a hydraulic pressurethat is greater than the hydraulic pressure produced by the one firstmanual hydraulic pressure source; and (c) a single typehydraulic-pressure distributor capable of supplying the hydraulicpressure produced by one of the second manual hydraulic pressure sourceand the at least one first manual hydraulic pressure source, to thebrake cylinders provided respectively for three wheels.

There are a case where the hydraulic pressure produced by the secondmanual hydraulic pressure source is supplied to all the brake cylindersprovided respectively for three wheels and a case where the hydraulicpressure produced by the at least one first manual hydraulic pressuresource is supplied to all the brake cylinders. In the latter case, thehydraulic pressure may be supplied to all the brake cylinders from thefirst manual hydraulic pressure source coupled to the second manualhydraulic pressure source, may be supplied to all the brake cylindersfrom the first manual hydraulic pressure source not coupled to thesecond manual hydraulic pressure source, and may be supplied to one ortwo of the three brake cylinders from the first manual hydraulicpressure source coupled to the second manual hydraulic pressure sourceand to the other two or one of the three brake cylinders from the firstmanual hydraulic pressure source not coupled to the second manualhydraulic pressure source.

(48) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels; and

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, compare a length of an arm extending from acenter of gravity of the vehicle to a position where right wheelscontact a road surface and a length of an arm extending from the centerof gravity of the vehicle to a position where left wheels contact a roadsurface with each other to supply a manual hydraulic pressure producedin response to a braking operation of a driver, to brake cylindersprovided respectively for three wheels of the four wheels such that asum of braking forces applied to front and rear wheels located on a sidenearer to a longer one of the arms is less than a sum of braking forcesapplied to front and rear wheels located on a side nearer to a shorterone of the arms.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (44).

(49) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle comprising a driver'sseat provided in a right portion of the vehicle in a forward direction,the plurality of hydraulic brakes each being configured to be operatedby a hydraulic pressure in a corresponding one of a plurality of brakecylinders to restrain rotation of a corresponding one of the fourwheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels, and

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to three of the frontleft and right and rear left and right brake cylinders such that a yawmoment causing the vehicle to turn in a left direction acts on thevehicle.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (45).

(50) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle comprising a driver'sseat provided in a right portion of the vehicle in a forward direction,the plurality of hydraulic brakes each being configured to be operatedby a hydraulic pressure in a corresponding one of a plurality of brakecylinders to restrain rotation of a corresponding one of the fourwheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels; and

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to the brake cylindersprovided respectively for the front right wheel, the front left wheel,and the rear right wheel.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (45).

(51) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle comprising a driver'sseat provided in a left portion of the vehicle in a forward direction,the plurality of hydraulic brakes each being configured to be operatedby a hydraulic pressure in a corresponding one of a plurality of brakecylinders to restrain rotation of a corresponding one of the fourwheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels; and

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to three of the frontleft and right and rear left and right brake cylinders such that a yawmoment causing the vehicle to turn in a right direction acts on thevehicle.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (45).

(52) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle comprising a driver'sseat provided in a left portion of the vehicle in a forward direction,the plurality of hydraulic brakes each being configured to be operatedby a hydraulic pressure in a corresponding one of a plurality of brakecylinders to restrain rotation of a corresponding one of the fourwheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels;

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to the brake cylindersprovided respectively for the front right wheel, the front left wheel,and the rear left wheel.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (45).

(53) A hydraulic brake system comprising:

a plurality of hydraulic brakes provided respectively for front left andright and rear left and right wheels of a vehicle and each configured tobe operated by a hydraulic pressure in a corresponding one of aplurality of brake cylinders to restrain rotation of a corresponding oneof the four wheels;

a power hydraulic system configured to: produce a hydraulic pressure bysupply of electric energy; control the produced hydraulic pressure; andsupply the controlled hydraulic pressure to the brake cylinders providedfor the respective four wheels;

a manual hydraulic system configured to, in case of an abnormality inthe power hydraulic system, supply a manual hydraulic pressure producedin response to a braking operation of a driver, to two brake cylindersprovided respectively for two wheels of the four wheels which arerespectively located at diagonal positions diagonal to each other, suchthat a braking force applied to a right wheel and a braking forceapplied to a left wheel are different from each other,

the manual hydraulic system further comprising: (i) at least one firstmanual hydraulic pressure source each configured to produce a hydraulicpressure related to an operating force of the driver for a brakeoperating member; (ii) a second manual hydraulic pressure sourceoperable by at least a hydraulic pressure produced by one of the atleast one first manual hydraulic pressure source and configured toproduce a hydraulic pressure that is greater than the hydraulic pressureproduced by the one first manual hydraulic pressure source; and (iii) asecond hydraulic-pressure supplier configured to supply the hydraulicpressure produced by the second manual hydraulic pressure source, to thetwo brake cylinders provided respectively for the two wheels located atthe diagonal positions.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (49).

(54) A hydraulic brake system comprising:

a power hydraulic pressure source configured to produce a hydraulicpressure by supply of electric energy;

at least one manual hydraulic pressure source configured to produce ahydraulic pressure by a braking operation of a driver;

a pressurization device provided between the power hydraulic pressuresource and one of the at least one manual hydraulic pressure source andcapable of supplying a hydraulic pressure that is greater than thehydraulic pressure produced by the one manual hydraulic pressure source,to the brake cylinder by utilizing the hydraulic pressure produced bythe power hydraulic pressure source; and

a pressurization-device check device configured to execute a check ofwhether an operation of the pressurization device is normal,

the pressurization-device check device comprising at least one of (i) afirst checker configured to execute the check based on a relationshipbetween the input-side hydraulic pressure in the pressurization deviceand the output-side hydraulic pressure in the pressurization device and(ii) a second checker configured to execute the check based on a changein the output-side hydraulic pressure in the pressurization device.

The hydraulic brake system in the present form can adapt any of thetechnical features in the forms (1) through (50).

(55) The first checker comprises a first normality determiner configuredto determine that the operation of the pressurization device is normal,when a predetermined relationship between the input-side hydraulicpressure in the pressurization device and the output-side hydraulicpressure in the pressurization device is established.

(56) The first checker comprises an input hydraulic pressure obtainerconfigured to obtain the input-side hydraulic pressure based on at leastone of the hydraulic pressure produced by the at least one manualhydraulic pressure source and a state of the braking operation.

(57) The hydraulic brake system further comprises an input-side cut-offvalve provided between the pressurization device and apressurization-device-coupled manual hydraulic pressure source as theone manual hydraulic pressure source, and

the second checker comprises an input-hindered-state check executerconfigured to execute the check in a state in which the input-sidecut-off valve is in a closed state.

(58) The pressurization device comprises: (a) a piston configured to bemoved by at least the hydraulic pressure produced by thepressurization-device-coupled manual hydraulic pressure source; (b) acontrol pressure chamber provided in front of the piston; (c) ahigh-pressure supply valve provided between the control pressure chamberand a high pressure chamber to which the power hydraulic pressure sourceis coupled,

the hydraulic brake system further comprises a high-pressure cut-offvalve provided between the pressurization device and the power hydraulicpressure source, and

the second checker further comprises a second normality determinerconfigured to determine that the operation of the pressurization deviceis normal when the hydraulic pressure in the control pressure chamberincreases in a case where the high-pressure cut-off valve is switchedfrom a closed state to an open state in a state in which the hydraulicpressure in the control pressure chamber is equal to or greater than aset pressure that is a hydraulic pressure causing the high-pressuresupply valve to be switched from the closed state to the open state.

(59) The high-pressure supply valve is configured to be switched fromthe closed state to the open state by a forward movement of the piston,

the pressurization device further comprises an input-sidehydraulic-pressure chamber coupled to the pressurization-device-coupledmanual hydraulic pressure source, and

the piston comprises an intra-piston communication passage formed in thepiston and coupling the control pressure chamber and the input-sidehydraulic-pressure chamber to each other, and the piston is configuredto be moved forward by the hydraulic pressure in the input-sidehydraulic-pressure chamber and brought into contact with thehigh-pressure supply valve to close the intra-piston communicationpassage.

(60) The second checker further comprises a pre-check output-sidehydraulic-pressure controller configured to control the hydraulicpressure in the control pressure chamber to move the piston forward toswitch the high-pressure supply valve from the closed state to the openstate.

(61) The pressurization device exhibits hysteresis, and the secondchecker further comprises a hysteresis-utilizing hydraulic-pressurecontroller configured to build up and then reduce the hydraulic pressurein the control pressure chamber to make the hydraulic pressure in thecontrol pressure chamber and the hydraulic pressure in the input-sidehydraulic-pressure chamber generally equal to each other.

(62) The second checker further comprises:

(a) a pressurization controller configured to execute pressurizationcontrol for building up the hydraulic pressure in the control pressurechamber such that the stepped piston is moved forward to establish aservo state in which the hydraulic pressure in the control pressurechamber is greater than the hydraulic pressure in the input-sidehydraulic-pressure chamber;

(b) a pressure-reduction controller configured to, after the hydraulicpressure in the control pressure chamber is built up by thepressurization controller, execute pressure-reduction control forreducing the hydraulic pressure in the control pressure chamber toestablish a non-servo state in which the hydraulic pressure in thecontrol pressure chamber is equal to the hydraulic pressure in theinput-side hydraulic-pressure chamber; and

(c) a servo-state-transition normality determiner configured todetermine that the operation of the pressurization device is normal, ina case where when the non-servo state is established by thepressure-reduction controller, and thereafter the high-pressure cut-offvalve is controlled to be switched from the closed state to the openstate, the non-servo state is switched to the servo state.

(63) The second checker further comprises:

(a) a pressurization controller configured to execute pressurizationcontrol for building up the hydraulic pressure in the control pressurechamber such that the stepped piston is moved forward to establish aservo state in which the hydraulic pressure in the control pressurechamber is greater than the hydraulic pressure in the input-sidehydraulic-pressure chamber; and

(b) a servo-state-pressurization normality determiner configured todetermine that the operation of the pressurization device is normal, ina case where when the servo state is established by the pressurizationcontroller, and thereafter the high-pressure cut-off valve is switchedfrom the closed state to the open state, the hydraulic pressure in thecontrol pressure chamber increases in the servo state.

(64) The pressurization device further comprises an input-sidehydraulic-pressure chamber coupled to the pressurization-device-coupledmanual hydraulic pressure source,

the high-pressure supply valve is configured to be switched from theclosed state to the open state by a forward movement of the piston,

the piston is configured to be moved forward by the hydraulic pressurein the input-side hydraulic-pressure chamber, and

the second checker comprises a pre-check input-side hydraulic-pressurepressurization controller configured to execute the pressurizationcontrol for the hydraulic pressure in the input-side hydraulic-pressurechamber such that the high-pressure supply valve is switched from theclosed state to the open state.

(65) The hydraulic brake system further comprises: an extra-pistoncommunication passage that bypasses the piston to couple the input-sidehydraulic-pressure chamber and the control pressure chamber to eachother; and an extra-piston communication cut-off valve provided in thecommunication passage.

Since the control pressure chamber and the input-side hydraulic-pressurechamber are coupled with each other by the extra-piston communicationpassage, the power hydraulic-pressure control device can be utilized inan open state of the communication cut-off valve to control thehydraulic pressure in the input-side hydraulic-pressure chamber.

(66) The second checker comprises: (a) a pressurization controllerconfigured to, in a state in which the communication cut-off valve iscontrolled to be in the open state, control the power hydraulic-pressurecontrol device to execute the pressurization control such that thehydraulic pressure in the input-side hydraulic-pressure chamber is builtup to a hydraulic pressure that moves the piston forward to switch thehigh-pressure supply valve from the closed state to the open state; (b)a communication-cut-off-valve controller configured to control thecommunication cut-off valve to be switched to a closed state in a statein which the hydraulic pressure in the input-side hydraulic-pressurechamber is controlled by the pressurization controller; and (c) aninput-hydraulic-pressure-control normality determiner configured todetermine that the operation of the pressurization device is normal,when the hydraulic pressure in the control pressure chamber increases ina case where the high-pressure cut-off valve is controlled to beswitched from the closed state to the open state after the communicationcut-off valve is controlled by the communication-cut-off-valvecontroller.

(67) One of the at least one manual hydraulic pressure source comprisesan assisting device configured to add an assisting force to a brakingoperation force of the driver and output a total force of the assistingforce and the braking operation force, and the hydraulic pressure in thecontrol pressure chamber of the pressurization device is supplied to theassisting device and functions as the assisting force.

The output-side hydraulic pressure in the pressurization device issupplied to the brake cylinder via the manual hydraulic pressure source(specifically, the manual hydraulic pressure source with the assistingdevice). A predetermined relationship is established between theoutput-side hydraulic pressure in the pressurization device and theoutput-side hydraulic pressure produced by the manual hydraulic pressuresource with the assisting device.

In this case, the output-side hydraulic pressure produced by the manualhydraulic pressure source with the assisting device can be employed asthe output-side hydraulic pressure in the pressurization device. Forexample, in a case where the control pressure chamber of thepressurization device is coupled to a rear hydraulic-pressure chamberformed at a rear of the pressurizing piston of the master cylinder withthe assisting device as the manual hydraulic pressure source with theassisting device, a hydraulic pressure in a pressure chamber in front ofthe pressurizing piston is related to a hydraulic pressure in the rearhydraulic-pressure chamber. Thus, the hydraulic pressure in the pressurechamber formed in front of the pressurizing piston of the mastercylinder with the assisting device can be used as the output-sidehydraulic pressure in the pressurization device, or alternatively theoutput-side hydraulic pressure in the pressurization device can beestimated on the basis of the hydraulic pressure in the pressure chamberformed in front of the pressurizing piston.

(68) The second checker further comprises a closed-space formerconfigured to, when the check is executed, cause a portion comprisingthe control pressure chamber to be a closed space.

(69) The hydraulic brake system further comprises a powerhydraulic-pressure control device configured to control the hydraulicpressure in the control pressure chamber by utilizing the hydraulicpressure produced by the power hydraulic pressure source.

The second checker may be configured to control the powerhydraulic-pressure control device to control the hydraulic pressure inthe control pressure chamber. The power hydraulic-pressure controldevice may comprise the pressurization linear control valve, thepressure-reduction linear control valve, and other similar devices.

It is noted that the power hydraulic-pressure control device can also becontrolled by the first checker, allowing checking in various modes.

(70) The hydraulic brake system may further comprise: a plurality ofbrake cylinders of a plurality of respective hydraulic brakes providedrespectively for a plurality of wheels of the vehicle to restrainrotations of the plurality of respective wheels; a common passage towhich the plurality of brake cylinders are connected and to which thepressurization device is connected; and a power hydraulic-pressurecontrol device capable of controlling a hydraulic pressure in the commonpassage by utilizing the hydraulic pressure produced by the powerhydraulic pressure source, wherein the second checker is configured toexecute the check in a state in which the control pressure chambercommunicates with the common passage.

(71) The pressurization-device check device further comprising anoperating checker configured to check whether the operation of thepressurization device is normal, when each of the plurality of hydraulicbrakes is in the working state.

(72) A hydraulic-pressure supply system comprising:

an external hydraulic pressure source;

a power hydraulic pressure source configured to produce a hydraulicpressure by supply of electric energy;

a pressurization device configured to be operated by the hydraulicpressure produced by the external hydraulic pressure source and capableof outputting a hydraulic pressure that is greater than the hydraulicpressure produced by the external hydraulic pressure source, byutilizing the hydraulic pressure produced by the power hydraulicpressure source;

a high-pressure cut-off valve provided between the pressurization deviceand the power hydraulic pressure source; and

a pressurization-device check device configured to execute a check ofwhether an operation of the pressurization device is normal,

the pressurization device comprising: (a) a piston configured to bemoved by the hydraulic pressure produced by the external hydraulicpressure source; (b) a control pressure chamber provided in front of thepiston; and (c) a high-pressure supply valve provided between thecontrol pressure chamber and a high pressure chamber to which the powerhydraulic pressure source is coupled,

the pressurization-device check device comprising apressurization-device normality determiner configured to determine thatthe operation of the pressurization device is normal when the hydraulicpressure in the control pressure chamber increases in a case where thehigh-pressure cut-off valve is switched from a closed state to an openstate in a state in which the hydraulic pressure in the control pressurechamber is equal to or greater than a set pressure that is a hydraulicpressure causing the high-pressure supply valve to be switched from theclosed state to the open state.

The hydraulic-pressure supply system in the present form can adapt anyof the technical features in the forms (1) through (68).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating an entirety of a vehicle on which ismounted a hydraulic brake system that is common to embodiments of thepresent invention.

FIG. 2 is a circuit diagram of a hydraulic brake circuit of a hydraulicbrake system according to embodiment 1 of the present invention.

FIG. 3 is a cross-sectional view illustrating a pressurization linearcontrol valve included in the hydraulic brake circuit.

FIGS. 4( a)-4(c) are views illustrating an input-side check valveincluded in the hydraulic brake circuit. FIG. 4( a) is a cross-sectionalview illustrating a cup seal check valve, FIG. 4( b-i) is across-sectional view illustrating a ball check valve, FIG. 4( b-ii) is across-sectional view taken along line A-A in FIG. 4( b-i), and FIG. 4(c) is a view conceptually illustrating a magnetic check valve.

FIG. 5 is a flow chart illustrating a hydraulic-pressure-supply-statecontrol program stored in a storage device of a brake ECU included inthe hydraulic brake system.

FIG. 6 is a view illustrating a state where the supply-state controlprogram is executed in the hydraulic brake system (in a case where thecontrol system works normally).

FIG. 7 is a view illustrating another state where the supply-statecontrol program is executed in the hydraulic brake system (in case of anabnormality in the control system).

FIG. 8 is a view illustrating another state where the supply-statecontrol program is executed in the hydraulic brake system (in case of anabnormality in the control system).

FIG. 9 is a view illustrating a state in which an ignition switch is OFFin the hydraulic brake system (in case of possible fluid leakage).

FIG. 10 is a hydraulic-brake circuit diagram of a hydraulic brake systemaccording to embodiment 2 of the present invention.

FIG. 11 is a hydraulic-brake circuit diagram of a hydraulic brake systemaccording to embodiment 3 of the present invention.

FIG. 12( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 4 of the present invention, and FIG. 12(b) is a view illustrating a right-hand drive vehicle on which thehydraulic brake system is mounted.

FIG. 13( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 5 of the present invention, and FIG. 13(b) is a view illustrating a left-hand drive vehicle on which thehydraulic brake system is mounted.

FIG. 14( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 6 of the present invention, and FIG. 14(b) is a view illustrating a left-hand drive vehicle on which thehydraulic brake system is mounted.

FIG. 15( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 7 of the present invention, and FIG. 15(b) is a view illustrating a right-hand drive vehicle on which thehydraulic brake system is mounted.

FIG. 16 is a hydraulic-brake circuit diagram of a hydraulic brake systemaccording to embodiment 8 of the present invention.

FIG. 17 is a view illustrating a state where the supply-state controlprogram is executed in the hydraulic brake system (in a case where thesystem works normally).

FIG. 18 is a view illustrating another state where the supply-statecontrol program is executed in the hydraulic brake system (in case of anabnormality in the control system).

FIG. 19 is a view illustrating another state where the supply-statecontrol program is executed in the hydraulic brake system (in case of anabnormality in the control system).

FIG. 20 is a view illustrating still another state where thesupply-state control program is executed in the hydraulic brake system(in case of possible fluid leakage).

FIG. 21 is a flow chart illustrating a check program stored in thestorage device of the brake ECU of the hydraulic brake system.

FIG. 22( a) is a view illustrating a state where the check program isexecuted in the hydraulic brake system (check 1), and FIG. 22( b) is adiagram representative of a relationship between an input-side hydraulicpressure and an output-side hydraulic pressure in the pressurizationdevice.

FIG. 23 is a view illustrating a state where the check program isexecuted in the hydraulic brake system (check 2-1).

FIG. 24 is a view illustrating another state where the check program isexecuted in the hydraulic brake system (check 2-2).

FIG. 25 is a diagram representative of change in a hydraulic pressure ina smaller-diameter-side chamber upon check 2.

FIG. 25( a) is a diagram representative of change in hydraulic pressurein a case where the hydraulic pressure in the smaller-diameter-sidechamber becomes a target hydraulic pressure.

FIG. 25( b) is a diagram representative of change in hydraulic pressurein a case where a high-pressure cut-off valve is switched from a closedstate to an open state.

FIG. 25( c) is a diagram representative of change in the hydraulicpressure in the smaller-diameter-side chamber upon a check differentfrom checks 1 and 2.

FIG. 26 is a flow chart partly illustrating the check program (in a casewhere check 2 is executed).

FIG. 27 is a circuit diagram of a hydraulic brake circuit of a hydraulicbrake system according to embodiment 9 of the present invention.

FIG. 28 is a cross-sectional view illustrating a mechanical/powerpressurization device included in the hydraulic brake circuit.

FIG. 29 is a circuit diagram of a hydraulic brake circuit of a hydraulicbrake system according to embodiment 10 of the present invention.

FIG. 30 is a cross-sectional view illustrating a pressurization deviceincluded in the hydraulic brake circuit.

FIG. 31 is a view illustrating a state where the check program isexecuted in the hydraulic brake system.

FIG. 32 is a view illustrating another state where the check program isexecuted in the hydraulic brake system.

FIG. 33 is a flow chart partly illustrating the check program (in a casewhere check 2 is executed).

FIG. 34( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 11 of the present invention, and FIG. 34(b) is a view illustrating a left-hand drive vehicle on which thehydraulic brake system is mounted.

FIG. 35( a) is a hydraulic-brake circuit diagram of a hydraulic brakesystem according to embodiment 12 of the present invention, and FIG. 35(b) is a view illustrating a right-hand drive vehicle on which thehydraulic brake system is mounted.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, there will be explained a hydraulic brake system accordingto embodiments of the present invention by reference to drawings. First,there will be explained a vehicle on which is mounted a hydraulic brakesystem as one example of the hydraulic brake system according toembodiments of the present invention. As illustrated in FIG. 1, thisvehicle is a hybrid vehicle that includes an electric motor and anengine each as a drive device. In the hybrid vehicle, front left andright wheels 2, 4 as drive wheels are driven by a drive device 10 thatincludes an electric drive device 6 and an internal-combustion(spark-ignition) drive device 8. A motive force (motive power) or adrive force (drive power) produced by the drive device 10 is transferredor transmitted to the front left and right wheels 2, 4 via drive shafts12, 14. The internal-combustion drive device 8 includes an engine 16 andan engine ECU 18 for controlling an operating state of the engine 16,and the electric drive device 6 includes an electric motor 20, a batterydevice 22, a motor generator 24, an electric power inverter 26, a motorECU 28, and a power split device 30. The electric motor 20, the motorgenerator 24, and the engine 16 are coupled to the power split device30, and these devices are controlled to selectively establish one of,e.g., a state in which only a driving torque of the electric motor 20 istransferred to an output member 32, a state in which both of a drivingtorque of the engine 16 and the driving torque of the electric motor 20to the output member 32, and a state in which an output of the engine 16is output to the motor generator 24 and the output member 32. The motiveforce transferred to the output member 32 is transferred to the driveshafts 12, 14 via a speed reducer and differential gears. The electricpower inverter (converter) 26 includes an inverter and is controlled bythe motor ECU 28. The control of a current supplied to the inverterswitches the electric power inverter 26 between at least a driving statein which the electric motor 20 is rotated by electric energy suppliedfrom the battery device 22 and a charging state in which the electricpower inverter 26 serves as a generator during the regenerative brakingto charge the battery device 22 with electric energy. In the chargingstate, a regenerative braking toque is applied to the front left andright wheels 2, 4. In this sense, the electric drive device 6 can beconsidered as a regenerative braking device.

The hydraulic brake system includes: brake cylinders 42 of hydraulicbrakes 40 provided for the respective front left and right wheels 2, 4;brake cylinders 52 of hydraulic brakes 50 provided for respective rearleft and right wheels 46, 48 (see FIG. 2, for example); and ahydraulic-pressure controller 54 configured to control hydraulicpressures in the respective brake cylinders 42, 52. Thehydraulic-pressure controller 54 is controlled by a brake ECU 56 that isconstituted principally by a computer. Also, the vehicle is providedwith a hybrid ECU 58. The hybrid ECU 58, the brake ECU 56, the engineECU 18, and the motor ECU 28 are communicably connected to one anothervia a CAN (car area network) 59, so that information is transmittedamong these devices as needed.

It is noted that the present hydraulic brake system is mountable notonly on the hybrid vehicle but also on a plug-in hybrid vehicle, anelectric vehicle, and a fuel-cell vehicle. In the case of the electricvehicle, the internal-combustion drive device 8 is not necessary. In thecase of the fuel-cell vehicle, a drive motor is driven by a fuel cellstack, for example. Also, the present hydraulic brake system ismountable on an internal-combustion drive vehicle. In such a vehicle notprovided with the electric drive device 6, a regenerative braking toqueis not applied to the drive wheels 2, 4, so that a regenerativecooperative control is not executed.

The hydraulic brake system will be hereinafter explained. In thefollowing description, each of the brake cylinders, the hydraulicbrakes, and electromagnetic open/close valves which will be describedbelow will be referred with a corresponding one of suffixes (FL, FR, RL,RR) indicative of the respective front left, front right, rear left, andrear right wheels where these cylinders, brakes, and valves should bedistinguished by their respective wheel positions. On the other hand,where these devices are collectively referred, or the distinction is notrequired, each of the cylinders, the brakes, and the valves will bereferred without such suffixes.

<Embodiment 1>

A hydraulic brake system according to embodiment 1 includes a brakecircuit illustrated in FIG. 2 in which the reference numeral “60”denotes a brake pedal as one example of a brake operating member, andthe reference numeral “62” denotes a master cylinder for producing ahydraulic pressure by operation of the brake pedal 60. The referencenumeral “64” denotes a power hydraulic pressure source that includes apump device 65 and an accumulator 66. The hydraulic brakes 40, 50 areactuated by the hydraulic pressures in the respective brake cylinders42, 52 to reduce rotations of the respective wheels. In the presentembodiment, each of the hydraulic brakes 40, 50 is a disc brake. It isnoted that each of the hydraulic brakes 40, 50 may be a drum brake.Also, the hydraulic brake system may be configured such that each of thehydraulic brakes 40 for the respective front wheels 2, 4 is a discbrake, and each of the hydraulic brakes 50 for the respective rearwheels 46, 48 is a drum brake.

The master cylinder 62 is a tandem cylinder that includes twopressurizing pistons 68, 69 and has pressure chambers 70, 72 located infront of the respective pressurizing pistons 68, 69. In the presentembodiment, each of the pressure chambers 70, 72 is one example of amanual hydraulic pressure source. The brake cylinder 42FL of thehydraulic brake 40FL for the front left wheel 2 is coupled to thepressure chamber 72 via a master passage 74 as one example of a manualpassage, and the brake cylinder 42FR of the hydraulic brake 40FR for thefront right wheel 4 is coupled to the pressure chamber 70 via a masterpassage 76 also as one example of the manual passage. Also, each of thepressure chambers 70, 72 is fluidically coupled with a reservoir 78 whena corresponding one of the pressurizing pistons 68, 69 reaches its backend position. An interior of the reservoir 78 is divided into fluidchambers 80, 82, 84 for storing working fluid or brake fluid. The fluidchambers 80, 82 are provided corresponding to the respective pressurechambers 70, 72, and the fluid chamber 84 is provided corresponding tothe pump device 65.

In the power hydraulic pressure source 64, the pump device 65 includes apump 90 and a pump motor 92. The pump 90 brings the working fluid fromthe fluid chamber 84 of the reservoir 78 and stores it into theaccumulator 66. The pump motor 92 is controlled such that a hydraulicpressure of the working fluid accumulated in the accumulator 66 fallswithin a predetermined range. Also, a relief valve 93 prevents anexcessive increase in pressure discharged from the pump 90.

A mechanical pressurization device 96 as one example of a pressurizationdevice is provided among the power hydraulic pressure source 64, themaster cylinder 62, and the brake cylinders 42, 52. The mechanicalpressurization device 96 includes a mechanical movable unit 98 as oneexample of a movable unit, an input-side check valve 99, and ahigh-pressure-side check valve 100. The mechanical movable unit 98includes a housing 102 and a stepped piston 104 that is fluid-tightlyand slidably fitted in the housing 102. The mechanical movable unit 98has: a larger-diameter-side chamber 110 near a large diameter portion ofthe stepped piston 104; and a smaller-diameter-side chamber 112 near asmall diameter portion of the stepped piston 104. The pressure chamber72 is fluidically coupled with the larger-diameter-side chamber 110. Inthe present embodiment, the pressure chamber 72 is one example of apressurization-device-coupled manual hydraulic pressure source (onemanual hydraulic pressure source). A high pressure chamber 114 coupledto the power hydraulic pressure source 64 is fluidically coupled withthe smaller-diameter-side chamber 112, and a high-pressure supply valve116 is disposed between the smaller-diameter-side chamber 112 and thehigh pressure chamber 114. The high-pressure supply valve 116 includes:a valve seat 122 formed on the housing 102; a valve element 120 movableto and away from the valve seat 122; and a spring 124. The spring 124urges the valve element 120 against the valve seat 122. Thehigh-pressure supply valve 116 is a normally closed valve. In thesmaller-diameter-side chamber 112, a valve opening member 125 isprovided opposite the valve element 120, and a spring 126 is disposedbetween the valve opening member 125 and the stepped piston 104. Thespring 126 urges the valve opening member 125 and the stepped piston 104such that the valve opening member 125 and the stepped piston 104 aremoved away from each other. The valve opening member 125 can also beconsidered as a constituent element of the high-pressure supply valve116.

Provided between a step of the stepped piston 104 and the housing 102 isa spring 128 (a return spring) that urges the stepped piston 104 in abackward direction. It is noted that a stopper, not shown, is providedbetween the stepped piston 104 and the housing 102 to limit a forwardend position of forward movement of the stepped piston 104. Also, thestepped piston 104 has an intra-piston communication passage 129 thatfluidically connects the larger-diameter-side chamber 110 and thesmaller-diameter-side chamber 112 to each other. An intra-piston checkvalve 130 is disposed in a portion of the intra-piston communicationpassage 129. The intra-piston check valve 130 inhibits a flow of theworking fluid from the larger-diameter-side chamber 110 to thesmaller-diameter-side chamber 112 and allows a flow of the working fluidfrom the smaller-diameter-side chamber 112 to the larger-diameter-sidechamber 110.

The high-pressure-side check valve 100 is disposed in a portion of ahigh-pressure supply passage 132 that fluidically connects the highpressure chamber 114 and the power hydraulic pressure source 64 to eachother. The high-pressure-side check valve 100 allows a flow of theworking fluid from the power hydraulic pressure source 64 to the highpressure chamber 114 when a hydraulic pressure produced by the powerhydraulic pressure source 64 is higher than a hydraulic pressure in thehigh pressure chamber 114, and is closed to inhibit flows in oppositedirections when the hydraulic pressure produced by the power hydraulicpressure source 64 is equal to or lower than the hydraulic pressure inthe high pressure chamber 114. Thus, even if an abnormality in theelectrical system lowers the hydraulic pressure produced by the powerhydraulic pressure source 64, lowering of a hydraulic pressure in thesmaller-diameter-side chamber 112 can be prevented.

The input-side check valve 99 is disposed in a portion of a bypasspassage 136 as one example of a movable-unit bypass passage thatbypasses the mechanical movable unit 98 to fluidically connect themaster passage 74 and an output side of the mechanical movable unit 98to each other (noted that the bypass passage 136 may connect the masterpassage 74 and the smaller-diameter-side chamber 112 to each other). Thebypass passage 136 can be considered as a passage that bypasses themechanical movable unit 98 to fluidically connect the master passage 74and a common passage 94 to each other. The input-side check valve 99allows a flow of the working fluid from the master passage 74 to theoutput side of the mechanical movable unit 98 and inhibits a flow of theworking fluid from the output side of the mechanical movable unit 98 tothe master passage 74. A valve opening pressure of the input-side checkvalve 99 is a set pressure. The set pressure is a value that isdetermined on the basis of a hydraulic pressure difference due to aheight difference between the master reservoir 78 and the brakecylinders 42 (noted that the master reservoir 78 is located on an upperside of the brake cylinders 42 in a vertical direction). The setpressure may be referred to as “height-difference-based set pressure”.

In the non-operated state of the brake pedal 60, the pressure chamber 72of the master cylinder 62 communicates with the master reservoir 78, sothat a hydraulic pressure in the pressure chamber 72 is nearly anatmospheric pressure. Also, a hydraulic pressure in each of the brakecylinders 42 is nearly the atmospheric pressure, but there is ahydraulic pressure difference between these components due to a heightdifference therebetween. Thus, where a valve opening pressure of theinput-side check valve 99 is set at a value that is determined on thebasis of the hydraulic pressure difference due to the height difference,it is possible to prevent an outflow of the working fluid from themaster reservoir 78 in the non-operated state of the brake pedal 60.Even if there is a leakage of the working fluid in the brake cylinders42 or components near the brake cylinders 42, it is possible to preventa flow of the working fluid from the master reservoir 78 to the brakecylinders 42. Also, when a brake actuating (operating) operation (thatis an operation for establishing a working state of each of thehydraulic brakes 40, 50 and that is normally a depressing operation) isperformed on the brake pedal 60, and the hydraulic pressure in thepressure chamber 72 is built up, a high-low pressure differential of theinput-side check valve 99 (which is a value obtained by subtracting acommon-passage-side hydraulic pressure from a master-cylinder-sidehydraulic pressure) becomes greater than the height-difference-based setpressure, and the input-side check valve 99 is switched to its openstate. As a result, a flow of the working fluid from the master cylinder62 to the brake cylinder is allowed.

The input-side check valve 99 may be constituted by one of valvesillustrated in FIG. 4, for example. For example, the input-side checkvalve 99 may be one of a cup seal check valve 99 x as illustrated inFIG. 4( a), a ball check valve 99 y as illustrated in FIG. 4( b), and amagnetic check valve 99 z as illustrated in FIG. 4( c).

In FIG. 4( a), the check valve 99 x includes: a housing 140 fixedlyprovided in the bypass passage 136; and an annular seal member 142supported by the housing 140. The seal member 142 is formed of amaterial allowing the seal member 142 to be easily deformed elasticallysuch as rubber. The seal member 142 is easily bent in a directionindicated by arrow X and is hard to be bent in a direction opposite thedirection indicated by arrow X. In the present embodiment, the masterpassage 74 is fluidically connected to an upstream portion of the checkvalve 99 x in the direction indicated by arrow X, and the common passage94 is fluidically connected to a downstream portion of the check valve99 x in the direction indicated by arrow X. The seal member 142 is notbent when the high-low pressure differential (i.e., a value obtained bysubtracting a hydraulic pressure in the common passage 94 from ahydraulic pressure in the master passage 74) is equal to or lower thanthe height-difference-based set pressure. The check valve 99 x is in itsclosed state, and the outflow of the working fluid from the masterreservoir 78 is inhibited. When the high-low pressure differentialbecomes higher than the height-difference-based set pressure, the sealmember 142 is bent. The check valve 99 x is switched to its open state,allowing the outflow of the working fluid from the master cylinder 62.It is noted that a flow of the working fluid in a reverse direction,i.e., in a direction directed from the common passage 94 toward themaster passage 74 is inhibited.

As illustrated in FIGS. 4( b)-(i), the check valve 99 y is a seatingvalve that includes (a) a housing 142, (b) a valve seat 143 formed inthe housing 142, and (c) a valve element 144 movable to and away fromthe valve seat 143. In the check valve 99 y, the valve element 144 isspherical in shape, and no springs are provided. Also, as illustrated inFIGS. 4( b)-(ii), a retaining portion 145 is provided on an oppositeside of the housing 142 from the valve seat 143. In the presentembodiment, as illustrated in FIGS. 4( b)-(i), the check valve 99 y isprovided in an orientation in which an axis L of the check valve 99 y isinclined by an angle θ with respect to a horizontal line H. Also, themaster passage 74 is fluidically connected to a downstream portion ofthe check valve 99 y in a direction of an axis-directional component Ga(=mgsin θ) of the gravity G (=mg) acting on the valve element 144, andthe common passage 94 is fluidically connected to an upstream portion ofthe check valve 99 y in the direction of the axis-directional componentGa.

In the check valve 99 y, when the high-low pressure differential (i.e.,a value obtained by subtracting the hydraulic pressure in thesmaller-diameter-side chamber 112 from a hydraulic pressure in themaster reservoir 78) is equal to or smaller than a magnitudecorresponding to the component Ga, the valve element 144 is seated onthe valve seat 143. The check valve 99 y is in its closed state, and aflow of the working fluid from the master reservoir 78 to the outputside of the pressurization device 96 is inhibited. When the high-lowpressure differential becomes greater than the magnitude correspondingto the component Ga, the valve element 144 is moved off the valve seat143, so that the check valve 99 y is switched to its open state, and aflow of the working fluid from the master passage 74 to the commonpassage 94 is allowed. In this state, the retaining portion 145 preventsthe valve element 144 from coming out of the check valve 99 y. Also,when a flow of the working fluid from the common passage 94 to themaster passage 74 is generated, a suction force moves the valve element144 toward the valve seat 143, so that the valve element 144 is seatedon the valve seat 143. In other words, the check valve 99 y is providedin an orientation in which the component Ga becomes a magnitudecorresponding to the height-difference-based set pressure (i.e., in theorientation in which the check valve 99 y is inclined by the angle θ).

In FIG. 4( c), the check valve 99 z includes a valve element 146 and avalve seat 147 and does not include any springs. Also, at least one ofthe valve element 146 and the valve seat 147 is a permanent magnetformed of a ferromagnetic material, so that the valve element 146 andthe valve seat 147 are moved toward each other by magnetic force. Themagnetic force (i.e., an attracting force) acting between the valveelement 146 and the valve seat 147 has a magnitude corresponding to theheight-difference-based set pressure. The master passage 74 and thecommon passage 94 are fluidically connected to the check valve 99 z suchthat a pressure differential between the hydraulic pressure in themaster passage 74 and the hydraulic pressure in the common passage 94acts in a direction opposite a direction of the magnetic force, that is,the master passage 74 is connected to an upstream portion of the checkvalve 99 z in a direction indicated by arrow Z, and the common passage94 is connected to a downstream portion of the check valve 99 z in thedirection indicated by arrow Z. When the high-low pressure differentialis equal to or lower than the height-difference-based set pressure, thecheck valve 99 z is in its closed state, and the outflow of the workingfluid from the master reservoir 78 is inhibited. When the high-lowpressure differential becomes greater than the height-difference-basedset pressure, the valve element 146 is moved off the valve seat 147against the magnetic force to switch the check valve 99 z to its openstate. This switching of the state allows the flow of the working fluidfrom the master passage 74 to the common passage 94. It is noted thatthe check valve 99 z may be provided with a retaining portion, notshown.

In the present embodiment, the bypass passage 136 and the intra-pistoncommunication passage 129 are one example of anintra-pressurization-device communication passage, the input-side checkvalves 99 x, 99 y, 99 z and other components are one example of a firstcheck valve, and the intra-piston check valve 130 is one example of asecond check valve.

It is noted that an input-side cut-off valve 148 is provided between themaster passage 74 and the mechanical pressurization device 96. Theinput-side cut-off valve 148 is a normally-open electromagneticopen/close valve that is in its open state when no current is suppliedto a coil of a solenoid of the valve (hereinafter may be simply referredto as “when no current is supplied to its solenoid”).

The brake cylinders 42FL, FR provided for the respective front left andright wheels 2, 4 and brake cylinders 52RL, RR provided for therespective rear left and right wheels 46, 48 are connected to the commonpassage 94 respectively by individual passages 150FL, FR, RL, RR each asa brake-side passage and an individual brake-side passage. Pressureholding valves (SHij: i=F, R, j=L, 153FL, FR, RL, RR are disposed in therespective individual passages 150FL, FR, RL, RR, and pressure reductionvalves (SRij: i=F, R, j=L, R) 156FL, FR, RL, RR are disposed between therespective brake cylinders 42FL, FR, 52RL, 52RR and the reservoir 78. Inthe present embodiment, each of the pressure holding valves 153FL, FRprovided for the respective front left and right wheels 2, 4 is anormally-open electromagnetic open/close valve that is in its open statewhen no current is supplied to its solenoid, and each of the pressureholding valves 153RL, RR for the respective rear left and right wheels46, 48 is a normally-closed electromagnetic open/close valve that is inits closed state when no current is supplied to its solenoid. Each ofthe pressure reduction valves 156FL, FR provided for the respectivefront left and right wheels 2, 4 is a normally-closed electromagneticopen/close valve that is in its closed state when no current is suppliedto its solenoid, and each of the pressure reduction valves 156RL, RRprovided for the respective rear left and right wheels 46, 48 is anormally-open electromagnetic open/close valve that is in its open statewhen no current is supplied to its solenoid.

In addition to the brake cylinders 42, 52, the power hydraulic pressuresource 64 and the mechanical pressurization device 96 are also connectedto the common passage 94. The power hydraulic pressure source 64 isconnected to the common passage 94 by a power hydraulic pressure passage170. A pressurization linear control valve (SLA) 172 is provided in thepower hydraulic pressure passage 170. The pressurization linear controlvalve 172 is a normally-closed electromagnetic open/close valve that isin its closed state when no current is supplied to its solenoid.Continuous control for a magnitude of a current supplied to the solenoidallows continuous control for a magnitude of the hydraulic pressure inthe common passage 94.

As illustrated in FIG. 3, the pressurization linear control valve 172includes: a seating valve including a valve element 180 and a valve seat182; a spring 184; and a solenoid (including a coil and a plunger) 186.An urging force F2 of the spring 184 urges the valve element 180 towardthe valve seat 182. Upon receipt of a current, the solenoid 186generates an electromagnetic driving force F1 that urges the valveelement 180 in a direction away from the valve seat 182. In thepressurization linear control valve 172, a pressure differential forceF3 related to a pressure differential between the power hydraulicpressure source 64 and the common passage 94 also urges the valveelement 180 in the direction away from the valve seat 182 (F1+F3: F2).Control for a current supplied to the solenoid 186 controls the pressuredifferential force F3 to control a hydraulic pressure in the powerhydraulic pressure passage 170. The pressurization linear control valve172 can be referred to as “output-hydraulic-pressure control valve” forcontrolling an output hydraulic pressure produced by the power hydraulicpressure source 64. It is noted that when a pressure-reduction controlis executed for the common passage 94, at least one of the pressurereduction valves 156 is opened or closed in a state in whichcorresponding at least one of the pressure holding valves 153 is in itsopen state. In the present embodiment, the pressurization linear controlvalve 172, at least one of the pressure reduction valves 156, and othersimilar components is one example of a power hydraulic-pressure controldevice.

The mechanical pressurization device 96 is connected to the commonpassage 94 by a servo-pressure passage 190. An output-side cut-off valve(SREG) 192 as one example of a pressurization-device cut-off valve isdisposed in the servo-pressure passage 190. The output-side cut-offvalve 192 is a normally-open electromagnetic open/close valve that is inits open state when no current is supplied to its solenoid.

The master passages 74, 76 are respectively connected to downstreamportions of the pressure holding valves 153FL, FR that are respectivelydisposed in the individual passages 150FL, FR connected to the frontleft and right wheels 2, 4. That is, the master passages 74, 76 bypassthe mechanical pressurization device 96 and the common passage 94 todirectly connect the respective pressure chambers 72, 70 and therespective brake cylinders 42 provided for the front left and rightwheels 2, 4 to each other (noted that each of the master passages 74, 76can be referred to as “direct manual passage”). The master cut-offvalves (SMCFL, FR) 194FL, FR each as a manual cut-off valve are disposedin portions of the respective master passages 74, 76. Each of the mastercut-off valves 194FL, FR is a normally-closed electromagnetic open/closevalve that is in its closed state when no current is supplied to itssolenoid. Also, a stroke simulator 200 is connected to the masterpassage 74 via a simulator control valve 202. The simulator controlvalve 202 is a normally-closed electromagnetic open/close valve.

In the present embodiment as described above, the pump device 65, thepressurization linear control valve 172, the master cut-off valves 194,the pressure holding valves 153, the pressure reduction valves 156, theinput-side cut-off valve 148, the output-side cut-off valve 192, andother similar components are one example of the hydraulic-pressurecontroller 54. The hydraulic-pressure controller 54 is controlled on thebasis of a command output from the brake ECU 56. As illustrated in FIG.1, the brake ECU 56 is constituted principally by a computer includingan executing portion, an input/output portion, and a storage device.Also, connected to the input/output portion include a brake switch 218,stroke sensors 220, a master-cylinder-pressure sensor 222, anaccumulator pressure sensor 224, a brake-cylinder-pressure sensor 226, alevel warning 228, wheel speed sensors 230, an ignition switch 234, andthe hydraulic-pressure controller 54.

The brake switch 218 is a switch that is switched from an OFF state toan ON state when the brake pedal 60 is operated.

Each of the stroke sensors 220 detects an operating stroke (STK) of thebrake pedal 60. In the present embodiment, two stroke sensors 220 areprovided to detect the operating stroke of the brake pedal 60 in thesame manner. Thus, even in the event of failure in one of the strokesensors 220, the other can detect the operating stroke.

The master-cylinder-pressure sensor 222 is configured to detect thehydraulic pressure in the pressure chamber 72 of the master cylinder 62(PMCFL) and provided in the master passage 74 in the present embodiment.

The accumulator pressure sensor 224 detects the pressure (PACC) of theworking fluid accumulated in the accumulator 66.

The brake-cylinder-pressure sensor 226 detects the hydraulic pressures(PWC) in the respective brake cylinders 42, 52 and is provided on thecommon passage 94. Since the brake cylinders 42, 52 and the commonpassage 94 communicate with each other in the open states of therespective pressure holding valves 153, the hydraulic pressure in thecommon passage 94 can be set at the hydraulic pressures in therespective brake cylinders 42, 52.

The level warning 228 is a switch that is switched to an ON state whenan amount of the working fluid stored in the master reservoir 78 becomesequal to or smaller than a predetermined amount. In the presentembodiment, the level warning 228 is switched to the ON state when theamount of the working fluid stored in one of the three fluid chambers80, 82, 84 becomes equal to or smaller than the predetermined amount.

The wheel speed sensors 230 are provided respectively for the front leftand right wheels 2, 4 and the rear left and right wheels 46, 48 todetect rotational speeds of the respective wheels. Also, a running speedof the vehicle is obtained on the basis of the rotational speeds of therespective four wheels.

The ignition switch (IGSW) 234 is a main switch of the vehicle.

The storage device stores various programs and tables, for example.

<Operations in Hydraulic Brake System>

In the present embodiment, states of the hydraulic pressures supplied tothe respective brake cylinders 42, 52 are controlled in a case where thehydraulic brake system works normally, in case of possible leakage, andin case where there is a malfunction or fault in the control system.

FIG. 5 is a flow chart illustrating a supply-state control program thatis executed at a predetermined time interval.

This supply-state control program begins with Step 1 (hereinafter,“Step” is omitted where appropriate) where it is determined whether abrake request is issued or not. When the brake switch 218 is in its ONstate or when an automatic brake is requested to be actuated, forexample, it is determined that the brake request has been issued, and apositive decision (YES) is made. Since the automatic brake may beactuated in a traction control, a vehicle stability control, afollowing-distance control, and a collision avoidance control, the brakerequest is assumed to be issued when conditions required for startingthese controls are satisfied. When the brake request is issued, it isdetermined at S2 whether there is a possibility of fluid leakage or not,and it is determined at S3 whether there is an abnormality in thecontrol system or not.

The presence or absence of the possibility of the fluid leakage isirrespective of a degree of the possibility of the fluid leakage and anamount of the fluid leakage. Thus, it is assumed that there is apossibility of the fluid leakage, when it is impossible to clearlydetermine that there is no fluid leakage even in a case where thepossibility of the fluid leakage is extremely low or in a case where anamount of the fluid having leaked is extremely small. Accordingly, evenwhere it has been determined that there is a possibility of the fluidleakage, the fluid leakage may not occur in reality (specifically,conditions (b)-(e) which will be described below may be satisfied by acause that differs from the fluid leakage).

For example, (a) when the level warning switch 228 is in its ON state,(b) when the braking operation is performed and when a predeterminedrelationship between a stroke of the brake pedal 60 and a hydraulicpressure in the master cylinder 62 is established, it is determined thatthere is no fluid leakage. On the other hand, when the hydraulicpressure in the master cylinder 62 is low relative to the stroke, it isdetermined that there is a possibility of the fluid leakage. Also, it isdetermined that there is a possibility of the fluid leakage (c) when adetection value of the accumulator pressure sensor 224 has not becomeequal to or larger than the fluid-leakage-determination threshold valueeven when the pump 90 is operated continuously for equal to or longerthan a predetermined length of time, (d) when a detection value of thebrake-cylinder-pressure sensor 226 is small relative to a detectionvalue of the master-cylinder-pressure sensor 222 in a case where theregenerative cooperative control is not executed, and (e) when it isdetermined, upon the preceding brake actuation, that there is apossibility of the fluid leakage (that is, when the hydraulic pressurein the master cylinder 62 is supplied to the brake cylinders 42 providedfor the respective front left and right wheels 2, 4, and the pumppressure is supplied to the brake cylinders 52 provided for therespective rear left and right wheels 46, 48), for example.

The abnormality in the control system means a state in which thehydraulic pressures in the respective brake cylinders 42, 52 or thehydraulic pressure in the common passage 94 cannot be controlled usingthe hydraulic pressure produced by the power hydraulic pressure source64.

For example, the abnormality in the control system includes: (i) a casewhere the components such as the electromagnetic open/close valve cannotbe operated as commanded (e.g., a case of a break in a wire(s) of theelectromagnetic open/close valve such as the pressurization linearcontrol valve 172 (including the pressure holding valves 153, thepressure reduction valves 156, the master cut-off valves 194, and theoutput-side cut-off valve 192)), (ii) a case where a detection valuerequired for controlling the hydraulic pressures in the respective brakecylinders 42, 52 cannot be obtained or cannot be precisely obtained(e.g., a case of a break in a wire(s) or a cable(s) of the sensor suchas the brake switch 218, the stroke sensors 220, themaster-cylinder-pressure sensor 222, the accumulator pressure sensor224, the brake-cylinder-pressure sensor 226, and the wheel speed sensors230), (iii) electric power (that can be also referred as “electricenergy” and “current”) cannot be supplied to components such as theelectromagnetic open/close valves and the sensors (e.g., a case of anabnormality in a power source of, e.g., the battery device 22 or a caseof a break in wires), and (iv) a case where high-pressure working fluidcannot be supplied to the power hydraulic pressure source 64 (e.g., acase of an abnormality in the pump motor 92 or a case where electricpower cannot be supplied to the pump motor 92 (including a case due tothe abnormality in the power source)).

When negative decisions (NO) are made at S2 and S3, that is, when thehydraulic brake system works normally (i.e., when it is determined thatthe control system works normally and there is no possibility of thefluid leakage in the present embodiment), a normal-condition control isexecuted at S4. The output hydraulic pressure produced by the powerhydraulic pressure source 64 is controlled by the pressurization linearcontrol valve 172 to supply the power control pressure to the commonpassage 94 and then to the brake cylinders 42, 52.

In the event of an abnormality in the control system, a positivedecision is made at S3, and this flow goes to S5 where supply of thecurrent to the solenoids of all the valves is stopped, so that thevalves are placed in their respective original positions. Also, the pumpmotor 92 is kept stopped.

When it is determined that there is a possibility of the fluid leakage,a positive decision (YES) is made at S2, and this flow goes to S6 wherethe hydraulic pressure in the master cylinder 62 is supplied to thebrake cylinders 42 provided for the respective front left and rightwheels 2, 4, and the output hydraulic pressure produced by the powerhydraulic pressure source 64 is controlled and supplied to the brakecylinders 52 provided for the respective rear left and right wheels 46,48. It is rare that there is an abnormality in the control system inaddition to a possibility of the fluid leakage. Thus, even when it isdetermined that there is a possibility of the fluid leakage, it isregarded that the control system works normally, making it possible tocontrol the valves and activate the pump motor 92.

Also, in the present embodiment, the automatic brake is inhibited frombeing operated when there is an abnormality in the control system orwhen there is a possibility of the fluid leakage.

1) In a Case where System Works Normally

As illustrated in FIG. 6, to the brake cylinders 42, 52 provided for therespective front left and right and rear left and right wheels 2, 4, 46,48, the hydraulic pressure produced by the power hydraulic pressuresource 64 is controlled and supplied, whereby the regenerativecooperative control is in principle executed (noted that the controlledhydraulic pressure may be referred to as “power control pressure”).

The regenerative cooperative control is executed for equalizing a totalbraking torque to a total required braking torque. The total brakingtorque is a sum of the regenerative braking toque applied to the drivewheels 2, 4 and a friction braking torque applied to the driven wheels46, 48 as well as to the drive wheels 2, 4.

The total required braking torque corresponds to a braking torquerequired by the driver, when the total required braking torque isobtained on the basis of values detected by the stroke sensors 220, thedetection value of the master-cylinder-pressure sensor 222, and othersimilar devices. Also, the total required braking torque corresponds toa braking torque required in the traction control and the vehiclestability control, when the total required braking torque is obtained onthe basis of a running state of the vehicle. A required regenerativebraking toque is determined on the basis of the total required brakingtorque (a requested value) and information which is supplied from thehybrid ECU 58 and which contains data indicative of a generator-sideupper limit value and a storage-side upper limit value. Thegenerator-side upper limit value is an upper limit value of theregenerative braking toque which is determined on the basis of, e.g., arotation speed of the electric motor 20, while the storage-side upperlimit value is an upper limit value of the regenerative braking toquewhich is determined on the basis of, e.g., a storage capacity of thebattery device 22. That is, the smallest one of the total requiredbraking torque, the generator-side upper limit value and thestorage-side upper limit value is determined as the requiredregenerative braking toque, and information representative of thedetermined required regenerative braking toque is supplied to the hybridECU 58.

The hybrid ECU 58 sends the motor ECU 28 information representative ofthe required regenerative braking toque. The motor ECU 28 then sends acontrol command to the electric power inverter 26 such that the brakingtorque applied to the front left and right wheels 2, 4 by the electricmotor 20 is made equal to the required regenerative braking toque. Theelectric motor 20 is controlled by the electric power inverter 26.

The motor ECU 28 sends the hybrid ECU 58 information representative ofan operating state of the electric motor 20 such as an actual rotationspeed. In the hybrid ECU 58, an actual regenerative braking toque isobtained on the basis of the actual operating state of the electricmotor 20, and information representative of a value of the actualregenerative braking toque is output to the brake ECU 56.

The brake ECU 56 determines a required hydraulic braking torque on thebasis of, for example, a value obtained by subtracting the actualregenerative braking toque from the total required braking torque, andthen controls the pressurization linear control valve 172, the pressurereduction valves 156 and other components to bring the brake-cylinderhydraulic pressure closer to a target hydraulic pressure correspondingto the required hydraulic braking torque.

During the regenerative cooperative control, in principal, all thepressure holding valves 153FL, FR, RL, RR provided for the front leftand right and rear left and right wheels 2, 4, 46, 48 are placed intheir respective open states, and all the pressure reduction valves156FL, FR, RL, RR in their respective closed states. Also, the mastercut-off valves 194FL, FR are placed in their respective closed states,the simulator control valve 202 in its open state, the input-sidecut-off valve 148 in its closed state, and the output-side cut-off valve192 in its closed state. The common passage 94 is disconnected orisolated from the mechanical pressurization device 96, and the brakecylinders 42FL, FR provided for the respective front left and rightwheels 2, 4 are decoupled or isolated from the master cylinder 62. Inthis state, the pressurization linear control valve 172 is controlled tocontrol the output hydraulic pressure produced by the power hydraulicpressure source 64, so that the power control pressure produced by thepower hydraulic pressure source 64 is supplied to the common passage 94and then to all the brake cylinders 42, 52. It is noted that when thehydraulic pressure in the common passage 94 is reduced, at least one ofthe pressure reduction valves 156FL, FR, RL, RR is controlled.

In the present embodiment as described above, the input-side cut-offvalve 148 is in the closed state in the normal operation.

Suppose that the input-side cut-off valve 148 is in the open state.

Since the output-side cut-off valve 192 is in the closed state, themechanical pressurization device 96 is a non-operating state inprincipal. However, the forward movement of the stepped piston 104 isallowed within a range in which the sum of a volume of the high pressurechamber 114, a volume of the smaller-diameter-side chamber 112, and avolume of the larger-diameter-side chamber 110 is kept generallyconstant. Since the simulator control valve 202 is in the open state, onthe other hand, when the hydraulic pressure in the master passage 74becomes higher than an actuating pressure of the stroke simulator 200,the stroke simulator 200 is activated. In the present embodiment,however, the actuating pressure of the stroke simulator 200 is lowerthan that of the mechanical movable unit 98.

When the brake actuating operation is performed on the brake pedal 60,and thereby the hydraulic pressure in the master passage 74 becomeshigher than the actuating pressure of the stroke simulator 200, thestroke simulator 200 is actuated to allow forward movement of the brakepedal 60. When the hydraulic pressure in the master passage 74thereafter becomes higher than the actuating pressure of the mechanicalmovable unit 98, the stepped piston 104 is moved forward, resulting inexcessive travel of the brake pedal 60, which causes discomfort to thedriver.

In the present embodiment, however, the input-side cut-off valve 148 isin the closed state, allowing the brake pedal 60 to move forward withthe operation of the stroke simulator 200. This movement of the brakepedal 60 prevents its excessive travel, thereby suppressing thediscomfort of the driver.

Also, since the input-side cut-off valve 148 is placed in the closedstate, it is possible to reduce vibrations and operating noises, forexample.

The actuating pressure of the stroke simulator 200 is a value that isdetermined by, e.g., sliding resistances such as a set load of a springand a friction between a piston and a housing of the stroke simulator200, and when a hydraulic pressure acting on the piston becomes higherthan an actuating pressure of the stroke simulator 200, the piston isallowed to be moved. This actuating pressure is determined by, e.g., theset load of the spring, and a frictional force.

The same principle applies to the actuating pressure of the mechanicalmovable unit 98. That is, the actuating pressure of the mechanicalmovable unit 98 is a value that is determined by, e.g., slidingresistances such as a set load of the spring 126 and a frictional forcebetween the stepped piston 104 and the housing 102.

In this state, if a slip of the wheels 2, 4, 46, 48 is excessively largeso as to satisfy an anti-lock control starting condition, the pressureholding valves 153 and the pressure reduction valves 156 are opened andclosed individually to control the hydraulic pressures in the respectivebrake cylinders 42, 52. As a result, a slipping state of each of thefront left and right and rear left and right wheels 2, 4, 46, 48 isoptimized.

Also, in a case where the hydraulic brake system is installed on avehicle not provided with the electric drive device 6, i.e., on avehicle in which the regenerative cooperative control is not executed,the devices such as the pressurization linear control valve 172 arecontrolled such that the total required braking torque and the hydraulicbraking torque are made equal to each other, in the case where thesystem works normally.

It is noted that components such as portions of the brake ECU 56 whichstore and execute the processing at S4 in thehydraulic-pressure-supply-state control program are one example of afirst input-side cut-off valve control device and a second input-sidecut-off valve control device. Also, these components can be referred toas a power control pressure supplier.

Also, components such as the portions of the brake ECU 56 which storeand execute the processing at S4, the power hydraulic pressure source64, the pressurization linear control valve 172, the common passage 94,the individual passages 150, and the brake cylinders 42, 52 are oneexample of a power hydraulic system.

2) In Case of Abnormality in Control System

As illustrated in FIGS. 7 and 8, the valves are placed back in theirrespective original positions.

No current is supplied to the solenoid 186 to establish the closed stateof the pressurization linear control valve 172, so that the powerhydraulic pressure source 64 is disconnected from the common passage 94.

Also, the master cut-off valves 194 are placed in the closed states, sothat the brake cylinders 42 are decoupled from the master cylinder 62.

Also, the input-side cut-off valve 148 and the output-side cut-off valve192 are placed in the open states, so that the mechanical pressurizationdevice 96 is connected to the master passage 74 and the common passage94.

Also, the pressure holding valves 153RL, RR are in the closed states,and the pressure holding valves 153FL, FR in the open states, so thatthe brake cylinders 42FL, FR provided for the respective front left andright wheels 2, 4 are connected to the common passage 94, and the brakecylinders 52RL, RR provided for the respective rear left and rightwheels 46, 48 are disconnected from the common passage 94.

Accordingly, the brake cylinders 42FL, FR provided for the respectivefront left and right wheels 2, 4 are actuated in the event of theabnormality in the control system. Thus, the generation of yaw momentcan be suppressed in a case where the center of gravity of the vehicleis located at generally a center of the vehicle in the right and leftdirection.

2-1) In a Case where Hydraulic Pressure in Larger-Diameter-Side Chamber110 is Equal to or Lower than Actuating Pressure of Mechanical MovableUnit 98

As illustrated in FIG. 7, when the hydraulic pressure in thelarger-diameter-side chamber 110 is equal to or lower than the actuatingpressure of the mechanical movable unit 98, the hydraulic pressure inthe pressure chamber 72 (may be referred to as “master hydraulicpressure” as the manual hydraulic pressure) is supplied to the commonpassage 94 via the master passage 74, the bypass passage 136, and theservo-pressure passage 190 and then to the brake cylinders 42 providedfor the respective front left and right wheels 2, 4.

Since the valve opening pressure of the input-side check valve 99 isconsiderably low, the working fluid can be speedily supplied to thebrake cylinders 42 in response to the operation for the brake pedal 60,resulting in shortened brake response time of each hydraulic brake 40.

2-2) In a Case where Hydraulic Pressure in Larger-Diameter-Side Chamber110 is Higher than Actuating Pressure of Mechanical Movable Unit 98

2-2-1) In a Case where Hydraulic Pressure of Working Fluid Accumulatedin Accumulator 66 is Higher than Actuation Allowing Pressure

In a case where the hydraulic pressure of the working fluid accumulatedin the accumulator 66 is higher than the set pressure, even where theoperation of the pump device 65 is stopped, the mechanical movable unit98 is allowed to be operated. The set pressure is such a pressure thatcan actuate the mechanical movable unit 98, in other words, themagnitude of the set pressure is such a magnitude that can supply thehydraulic pressure to the high pressure chamber 114 of the mechanicalmovable unit 98. Thus, the set pressure can be considered to be higherthan the hydraulic pressure in the high pressure chamber 114(specifically in the smaller-diameter-side chamber 112). The setpressure can be referred to as “actuation allowing pressure”.

As illustrated by solid lines in FIG. 8, the stepped piston 104 is movedforward by the hydraulic pressure in the larger-diameter-side chamber110 to be brought into contact with the valve opening member 125,thereby switching the high-pressure supply valve 116 to the open state.The smaller-diameter-side chamber 112 is decoupled from thelarger-diameter-side chamber 110, and the high-pressure working fluid issupplied from the accumulator 66 to the high pressure chamber 114 viathe high-pressure-side check valve 100 and then to thesmaller-diameter-side chamber 112. The hydraulic pressure in thesmaller-diameter-side chamber 112 is made higher than the hydraulicpressure in the master cylinder 62 and supplied to the common passage 94via the output-side cut-off valve 192 being in the open state and thento the brake cylinders 42FL, 42FR provided for the respective front leftand right wheels 2, 4, via the respective pressure holding valves 153FL,FR.

Assuming that the actuating pressure is zero, a hydraulic pressure Poutin the smaller-diameter-side chamber 112 is a value obtained bymultiplying a hydraulic pressure Pin in the master cylinder 62 (i.e.,the hydraulic pressure in the larger-diameter-side chamber 110) by aratio (Sin/Sout) between a pressure receiving area Sin of the largediameter portion of the stepped piston 104 and a pressure receiving areaSout of the small diameter portion of the stepped piston 104. That is,the hydraulic pressure Pout is represented by the following equation:Pout=Pin−(Sin/Sout)This hydraulic pressure Pout may be referred to as “servo pressure”.Thus, the smaller-diameter-side chamber 112 may be referred to as“control pressure chamber”.

It is noted that, since the mechanical pressurization device 96 isoperated by the hydraulic pressure in the pressure chamber 72, themechanical pressurization device 96 can be considered to be a manualhydraulic pressure source in a broad sense. In the present embodiment,the pressure chamber 72 is one example of apressurization-device-coupled manual hydraulic pressure source as afirst manual hydraulic pressure source, and the mechanicalpressurization device 96 is one example of a second manual hydraulicpressure source.

2-2-2) In a Case where Hydraulic Pressure of Working Fluid Accumulatedin Accumulator 66 is Equal to or Lower than Actuation Allowing Pressure

In a case where the hydraulic pressure of the working fluid accumulatedin the accumulator 66 is equal to or lower than the actuation allowingpressure, as in the state illustrated in FIG. 7, the master hydraulicpressure in the pressure chamber 72 of the master cylinder 62 issupplied to the brake cylinders 42 provided for the respective frontleft and right wheels 2, 4 via the master passage 74, the bypass passage136, the servo-pressure passage 190, and the common passage 94.

Meanwhile, when the hydraulic pressure of the working fluid accumulatedin the accumulator 66 is reduced by the operation of the mechanicalmovable unit 98 and becomes lower than the actuation allowing pressure,the supply of the working fluid from the accumulator 66 to the highpressure chamber 114 is stopped. This makes it hard for the mechanicalmovable unit 98 to be operated or actuated. For example, when the brakeis pumped, more working fluid accumulated in the accumulator 66 isconsumed, making the accumulator pressure lower than the actuationallowing pressure. The forward movement of the stepped piston 104 isinhibited (it is considered that the stepped piston 104 is moved forwarduntil the stepped piston 104 is brought into contact with the stopper,and then the forward movement of the stepped piston 104 is inhibited),so that the hydraulic pressure in the smaller-diameter-side chamber 112is not built up any higher, that is, the mechanical movable unit 98 ismade unable to exhibit a boosting function. When the hydraulic pressurein the pressure chamber 72 becomes higher than the hydraulic pressure inthe smaller-diameter-side chamber 112, as indicated by a broken line inFIG. 8, the hydraulic pressure in the pressure chamber 72 of the mastercylinder 62 is supplied to the common passage 94 via the bypass passage136 and the servo-pressure passage 190. The hydraulic pressure in thepressure chamber 72 of the master cylinder 62 is supplied to the brakecylinders 42FL, 42FR provided for the respective front left and rightwheels 2, 4, without being boosted.

Also, since the pressure holding valves 153RL, RR are in the closedstates, the hydraulic pressure in the mechanical movable unit 98 isinhibited from being supplied to the brake cylinders 52RL, 52RR providedfor the respective rear left and right wheels 46, 48. This reduces apossibility of a fluid shortage and a shortage of pressure buildup forthe brake cylinders 42FL, FR provided for the respective front left andright wheels 2, 4.

Moreover, the volume of the pressure chamber 72 may be increased in themaster cylinder 62. Where the volume of the pressure chamber 72 isincreased, even when the working fluid is supplied to both of the brakecylinders 42FL, FR provided for the respective front left and rightwheels 2, 4, the fluid shortage can be avoided. In this case, the strokeof the brake pedal 60 operated by the driver may be larger.

In the present embodiment, the configuration in which each of thepressure holding valves 153FL, FR is the normally open valve, theconfiguration in which each of the input-side cut-off valve 148 and theoutput-side cut-off valve 192 is the normally open valve, portions ofthe brake ECU 56 which store and execute the processing at S5, and so onare one example of an abnormal-case servo-pressure supply device. Also,portions of the brake ECU 56 which store and execute the processing atS5 are one example of a servo pressure supplier.

3) In Case of Detection of Possibility of Fluid Leakage

As illustrated in FIG. 9, the pressure holding valves 153FL, FR for therespective front left and right wheels 2, 4 are placed in the closedstates, and the pressure holding valves 153RL, RR for the respectiverear left and right wheels 46, 48 in the open states. Also, the mastercut-off valves 194FL, FR are placed in the open states, and theinput-side cut-off valve 148, the output-side cut-off valve 192, and thesimulator control valve 202 in the closed states. Also, all the pressurereduction valves 156 are placed in the closed states.

The hydraulic pressures in the pressure chambers 72, 70 of the mastercylinder 62 are respectively supplied to the brake cylinders 42FL, FRprovided for the respective front left and right wheels 2, 4, and thehydraulic pressure produced by the pump device 65 is controlled andsupplied to the brake cylinders 52RL, RR provided for the respectiverear left and right wheels 46, 48.

Since the pressure holding valves 153FL, FR for the respective frontleft and right wheels 2, 4 are thus in the closed states, the brakecylinders 42FL, FR provided for the respective front left and rightwheels 2, 4 are independent of each other. Also, the brake cylinders42FL, FR provided for the respective front left and right wheels 2, 4are decoupled or isolated from the brake cylinders 52RL, RR provided forthe respective rear left and right wheels 46, 48. That is, the brakecylinders provided for the respective front wheels 2, 4, and the brakecylinders provided for the respective rear wheels 46, 48 are isolatedfrom each other, and the brake cylinders provided respectively for thefront left wheel 2 and the front right wheel 4 are isolated from eachother. That is, three brake lines are isolated from one another,specifically a brake line 250FL including the brake cylinder 42FLprovided for the front left wheel 2, a brake line 250FR including thebrake cylinder 42FR provided for the front right wheel 4, and a brakeline 250R including the brake cylinders 52RL, RR provided for therespective rear left and right wheels 46, 48 are isolated from oneanother. Accordingly, even if one of these three brake lines suffersfrom the fluid leakage, the other brake lines are not influenced by thefluid leakage.

In this sense, the pressure holding valves 153FL, FR have a function asa separate valve for separating the brake lines 250FR, FL, R from oneanother.

In the present embodiment, the brake line 250FR includes the brakecylinder 42FR, the master passage 76, the pressure chamber 70, and thefluid chamber 80. The brake line 250FL includes the brake cylinder 42FL,the master passage 74, the pressure chamber 72, and the fluid chamber82. The brake line 250R includes the brake cylinders 52RL, RR, theindividual passages 150RL, RR, the power hydraulic pressure source 64,and the fluid chamber 84. Therefore, the configuration in which thebrake lines 250FR, FL, R are independent of one another means that thefluid chambers 80, 82, 84 of the reservoir 78 are also independent ofone another.

In the present embodiment, portions of the brake ECU 56 which store andexecute the processing at S6 and so on are one example of amanual-hydraulic-pressure and power-control-pressure supplier.

Also, even in a case where there is no possibility of the fluid leakage,when the hydraulic pressure of the working fluid accumulated in theaccumulator 66 is lower than the actuation allowing pressure, the statein FIG. 9 can be established. The situation in which the hydraulicpressure of the working fluid accumulated in the accumulator 66 becomeslower than the actuation allowing pressure is considered to be causedby, e.g., the abnormality in the pump device 65 (noted that theelectromagnetic open/close valve can be controlled), but in this case itis determined that the situation is caused by the abnormality in thecontrol system, and the state in FIG. 7 or 8 is established. However, inthe state in FIG. 7 or 8, the mechanical movable unit 98 cannot beoperated, and as indicated by the broken line in FIG. 8 the hydraulicpressure in the pressure chamber 72 of the master cylinder 62 issupplied to the brake cylinders 42FL, FR. When the state in FIG. 9 isestablished, in contrast, the pressure chambers 72, 70 are coupled tothe respective brake cylinders 42FL, FR, thereby reducing shortage ofthe hydraulic pressure. It is noted that, in a case where the hydraulicpressures in the brake cylinders 52RL, RR provided for the respectiverear left and right wheels 46, 48 cannot be effectively controlled dueto a low hydraulic pressure of the working fluid accumulated in theaccumulator 66, the pressure holding valves 153RL, RR are preferablyplaced in the closed states, with the pressurization linear controlvalve 172 being in the closed state.

4) In a Case of Release of Hydraulic Brake

Upon release of the braking operation, no current is supplied to thesolenoids of all the valves, so that all the valves are placed back inthe original positions in FIG. 2. In the mechanical pressurizationdevice 96, the stepped piston 104 is located at its back end position(or moved back to the back end position). The stepped piston 104 isspaced apart from the valve opening member 125, so that the intra-pistoncommunication passage 129 is opened. The hydraulic pressures in thebrake cylinders 42FL, FR provided for the respective front left andright wheels 2, 4 are returned to the master cylinder 62 (i.e., themaster reservoir 78) via the intra-piston communication passage 129 andthe intra-piston check valve 130. Also, the hydraulic pressures in thebrake cylinders 52RL, RR provided for the respective rear left and rightwheels 46, 48 are returned to the reservoir 78 via the respectivepressure reduction valves 156.

5) OFF State of Ignition Switch 234

No current is supplied to the solenoids of all the valves, so that allthe valves are placed back in the original positions in FIG. 2.

a) As illustrated in FIG. 2, since the pressurization linear controlvalve 172 is in the closed state, the power hydraulic pressure source 64is disconnected from the common passage 94. Thus, even in the event offluid leakage at a position downstream of the common passage 94 (e.g.,the brake cylinders 42FL, FR), it is possible to prevent an outflow ofthe working fluid from the fluid chamber 84 of the reservoir 78 via thepower hydraulic pressure passage 170.

b) Since the master cut-off valves 194 are in the closed states, even iffluid leakage occurs near the brake cylinders 42FL, FR provided for therespective front left and right wheels 2, 4, it is possible to preventan outflow of the working fluid from the fluid chambers 80, 82 of thereservoir via the master passages 74, 76.

c) Since the input-side check valve 99 and the intra-piston check valve130 are provided, even if fluid leakage occurs at a position downstreamof the common passage 94, it is possible to prevent an outflow of theworking fluid from the fluid chamber 82 of the master reservoir 78 viathe mechanical pressurization device 96. Even in the event of fluidleakage at a position downstream of the common passage 94, the outflowof the working fluid from the fluid chamber 82 of the master reservoir78 via the intra-piston communication passage 129 is inhibited, and theinput-side check valve 99, the intra-piston check valve 130, and so onare one example of an outflow preventing device 260.

As thus described, in an OFF state of the ignition switch 234 in thepresent embodiment, even if fluid leakage occurs at a positiondownstream of the common passage 94, it is possible to reliably preventan outflow of the working fluid from the fluid chambers 80, 82, 84 ofthe master reservoir 78, allowing the hydraulic brakes 40, 50 to beoperated satisfactorily.

The input-side check valve 99, the intra-piston check valve 130, and soon are one example of the outflow preventing device 260 in the presentembodiment. Nevertheless, in addition to these devices, the outflow fromthe master reservoir 78 can be prevented by devices such as the mastercut-off valves 194, the pressurization linear control valve 172, and thepressure holding valves 153RL, RR.

<Embodiment 2>

As illustrated in FIG. 10, an outflow preventing device 270 is providedat any position between a portion of the common passage 94 which isconnected to the servo-pressure passage 190 and a portion of theindividual passage 150FR in which the pressure holding valve 153FR isprovided. The other configurations are the same as those inembodiment 1. The outflow preventing device 270 includes a first checkvalve 272 and a second check valve 274 which are provided parallel toeach other. Like the input-side check valve 99 in embodiment 1, thefirst check valve 272 is configured such that its valve opening pressureis set at the height-difference-based set pressure. Like theintra-piston check valve 130 in embodiment 1, the second check valve 274allows a flow of the working fluid from the brake cylinder 42FR to themaster reservoir 78 and inhibits a flow of the working fluid from themaster reservoir 78 to the brake cylinder 42FR. The outflow preventingdevice 270 can prevent an outflow of the working fluid from thereservoir fluid chamber 82 to the brake cylinder 42FR via the mechanicalpressurization device 96 when the brake actuating operation is not beingperformed on the brake pedal 60. In particular, the outflow preventingdevice 270 can prevent an outflow of the working fluid from thereservoir fluid chamber 82 in the event of fluid leakage near the brakecylinder 42FR provided for the front right wheel 4, thereby reducing apossibility of a shortage of the braking force when the hydraulic brakes40, 50 are operated. It is noted that the intra-piston check valve isnot necessary in the mechanical pressurization device 96. Also, aninput-side check valve 276 may have any valve opening pressure. Thevalve opening pressure of the input-side check valve 276 may be set at amagnitude that is not related to the hydraulic pressure difference dueto the height difference.

<Embodiment 3>

As illustrated in FIG. 11, an outflow preventing device 280 may beprovided in the servo-pressure passage 190 and in the mechanicalpressurization device 96 at a position between the smaller-diameter-sidechamber 112 and a portion of the servo-pressure passage 190 which isconnected to the bypass passage 136. As in embodiment 2, the outflowpreventing device 280 includes a first check valve 282 and a secondcheck valve 284 which are provided parallel to each other. The otherconfigurations are the same as those in embodiment 1. The outflowpreventing device 280 can inhibit the outflow of the working fluid fromthe fluid chamber 82 of the master reservoir 78 via the intra-pistoncommunication passage 129 when the brake actuating operation is notbeing performed on the brake pedal 60. The outflow preventing device 280may be provided at any position in the servo-pressure passage 190. Forexample, the outflow preventing device 280 may be provided downstream ofthe bypass passage 136 and may be provided downstream of the output-sidecut-off valve 192, i.e., on a side of the output-side cut-off valve 192which is nearer to the common passage.

<Other Embodiments>

It is noted that the brake circuit may have any design.

For example, the mechanical pressurization device 96 may be directlyconnected to the master passage 74. In other words, the input-sidecut-off valve 148 is not essential. The outflow preventing device is notessential, either. Also, providing both of the master cut-off valves194FL, FR as the normally closed valves is not essential, and at leastone of the master cut-off valves 194FL, FR may be a normally open valve.

Also, the system may be configured such that at least one of thepressure holding valves 153RL, RR for the respective rear left and rightwheels 46, 48 is a normally-open electromagnetic open/close valve, and acorresponding at least one of the pressure reduction valves 156RL, RR isa normally-closed electromagnetic open/close valve. In the presentembodiment, in the event of the abnormality in the control system, theoutput hydraulic pressure in the mechanical pressurization device 96 canbe supplied to three or four of the brake cylinders 42, 52. In the eventof the abnormality in the control system, brake cylinders to be coupledto the mechanical pressurization device 96 can be determined by acapability of the supply of the working fluid based on, e.g., the volumeof the pressure chamber 72 of the master cylinder 62. Also, when avolume of the master cylinder 62 is increased, the operating stroke ofthe driver on the brake pedal 60 may be increased, or a reaction forcemay be increased (that is, a larger operating force may be required).Nevertheless, the volume of the master cylinder 62 may be suitablydetermined with consideration of, e.g., an operation feeling of thedriver and the number of hydraulic brakes to be operated in the event ofthe abnormality in the control system.

<Embodiment 4>

As illustrated in FIG. 12( a), the system is configured such that apressure holding valve 153RR1 corresponding to a brake cylinder 52RRprovided for the rear right wheel 48 that is one of the rear left andright wheels 46, 48 is a normally-open electromagnetic open/close valve,and a pressure reduction valve 156RR1 for the rear right wheel 48 is anormally-closed electromagnetic open/close valve. In the presentembodiment, in the event of the abnormality in the control system, theoutput hydraulic pressure in the mechanical pressurization device 96 issupplied to the brake cylinders 42FL, FR, 52RR provided respectively forthe front left and right wheels 2, 4 and the rear right wheel 48. Asillustrated in FIG. 12( b), in a relatively small-sized vehicle that hasa driver's seat in its right portion in a forward direction (that is, asteering member 300 is provided in the right portion in the forwarddirection), namely a right-hand drive vehicle, a center of gravity G1 ofthe entire vehicle including the driver may be located on the right of acenter line of the vehicle in the right and left direction. The otherconfigurations are the same as those in embodiment 1. In this vehicle, alength rL of an arm extending from the center of gravity G1 to a contactposition where the left wheels 2, 46 contact a road surface is longerthan a length rR of an arm extending from the center of gravity G1 to acontact position where the right wheels 4, 48 contact the road surface(rL>rR). When the hydraulic pressure in the mechanical pressurizationdevice 96 is supplied to the brake cylinders 42FL, FR provided for therespective front left and right wheels 2, 4 in the event of theabnormality in the control system in this configuration, a yaw moment yin a left-turning direction acts on the vehicle.y=rR·(F _(FR))−rL·(F _(FL))<0

To address this yaw moment, in the present embodiment, in the event ofthe abnormality in the control system, the servo pressure as thehydraulic pressure in the mechanical pressurization device 96 issupplied to the brake cylinders 42FL, FR provided for the respectivefront left and right wheels 2, 4 and the brake cylinder 52RR providedfor the rear right wheel 48. The respective hydraulic pressures in thebrake cylinders provided respectively for three wheels 42FL, FR, RR aregenerally equal to one another (P_(FL)=P_(FR)=P_(RF)). Thus, the sum ofbraking forces (i.e., forces acting on positions between tires and theroad surface) caused by the hydraulic pressures supplied to the brakecylinders 42FL, 52RL provided for the respective left wheels 2, 46(noted that the hydraulic pressure is not supplied to the brake cylinder52RL provided for the rear left wheel 46) is smaller than the sum ofbraking forces caused by the hydraulic pressures supplied to the brakecylinders 42FR, RR provided for the respective right wheels 4, 48(F_(FL)<F_(FR)+F_(RR)).

An absolute value of the yaw moment y acting on this vehicle isrepresented by the following equation:|y|=|rR·(F _(FR) +F _(RR))−rL·(F _(FL))|Since the arm rL is longer than the arm rR as described above, it ispossible to reduce the absolute value of the yaw moment y acting on thevehicle.

In the present embodiment as described above, the servo pressure in themechanical pressurization device 96 is supplied to the brake cylindersprovided respectively for the three wheels of the four front left andright and rear left and right wheels in the event of the abnormality inthe control system, so that the sum of the braking forces acting on therespective left wheels 2, 46 and the sum of the braking forces acting onthe respective right wheels 4, 48 are not equal to each other. However,in a case where the center of gravity G is located off the center of thevehicle in the right and left direction, the servo pressure in themechanical pressurization device 96 is distributed such that the sum ofbraking forces acting on wheel(s) nearer to the shorter arm extendingfrom the center of gravity G is larger than the sum of braking forcesacting on wheel(s) nearer to the longer arm extending from the center ofgravity G. Thus, the generation of the yaw moment can be suppressed inthe event of the abnormality in the control system. In the presentembodiment, the master cylinder 62, the mechanical pressurization device96, the common passage 94, the individual passages 150FL, FR, RR, thenormally-open pressure holding valves 153FL, FR, RR1, the brakecylinders 42FL, FR, 52RR, and so on are one example of a manualhydraulic system. This manual hydraulic system includes a single-typehydraulic-pressure distributor. It is noted that, while the outputhydraulic pressure in the mechanical pressurization device 96 is theservo pressure as described above, the servo pressure can be consideredto be a manual hydraulic pressure in a broad sense.

It is noted that the intra-piston check valve 130 and the input-sidecut-off valve 148 are not essential in the present embodiment.

<Embodiment 5>

In a hydraulic brake circuit illustrated in FIG. 13( a), a pressureholding valve 153RL2 corresponding to the brake cylinder 52RL providedfor the rear left wheel 46 that is one of the rear left and right wheels46, 48 is a normally open valve, and a pressure reduction valve 156RL2for the rear left wheel 46 is a normally closed valve. In the presentembodiment, in the event of the abnormality in the control system, theservo pressure in the mechanical pressurization device 96 is supplied tothe brake cylinders 42FL, FR, 52RL respectively for the front left andright wheels 2, 4 and the rear left wheel 46. As illustrated in FIG. 13(b), in a vehicle that has a driver's seat in its left portion in theforward direction (that is, a steering member 302 is provided in theleft portion in the forward direction), namely a left-hand drivevehicle, a center of gravity G2 of the entire vehicle including thedriver may be located on the left of a center line of the vehicle in theright and left direction. The other configurations are the same as thosein embodiment 1.

In the present embodiment, an absolute value of the yaw moment y actingon the vehicle in the event of the abnormality in the control system isrepresented by the following equation:|y|=|rR(F _(FR))−rL(F _(FL) +F _(RL))|In this case, the sum of braking forces acting on the respective rightwheels 4, 48 is smaller than the sum of braking forces acting on therespective left wheels 2, 46 (F_(FR)<F_(FL)+F_(RL)), and an arm rRextending from the center of gravity G2 to a contact position where theright wheels 4, 48 contact the road surface is longer than an arm rLextending from the center of gravity G2 to a contact position where theleft wheels 2, 46 contact the contact position (rR>rL), making itpossible to reduce the absolute value of the yaw moment y acting on thevehicle. In the present embodiment, the master cylinder 62, themechanical pressurization device 96, the common passage 94, theindividual passages 150FL, FR, RL, the normally-open pressure holdingvalves 153FL, FR, RL2, the brake cylinders 42FL, FR, 52RR, and so on areone example of a manual hydraulic system. This manual hydraulic systemincludes a single-type hydraulic-pressure distributor.<Embodiment 6>

In a hydraulic brake circuit in FIG. 14( a), a master cut-off valve194FR3 corresponding to the brake cylinder 42FR provided for the frontright wheel 4 is a normally open valve, and a pressure holding valve153FR3 is a normally closed valve. Also, a pressure holding valve 153RR3corresponding to the brake cylinder 52RR provided for the rear rightwheel 48 is a normally open valve, and a pressure reduction valve 156RR3is a normally closed valve. In the event of an abnormality in thecontrol system, a master pressure is supplied to the brake cylinder 42FRprovided for the front right wheel 4, and the servo pressure in themechanical pressurization device 96 is supplied to the brake cylinders42FL, 52RR provided respectively for diagonal wheels (i.e., the frontleft wheel 2 and the rear right wheel 48).

A right-turning-directional yaw moment y acting on a vehicle that has adriver's seat in its left portion in the forward direction (i.e., avehicle having a steering wheel 302 in its left portion) is representedby the following equation:y=rR(F _(FR) +F _(RR))−rL(F _(FL))In this equation, a hydraulic pressure Pm in the master cylinder 62 islower than a servo pressure Pb in the mechanical pressurization device96 (Pm<Pb). Also, where the brake-cylinder hydraulic pressures are equalto one another, the braking force acting on the rear wheel is smallerthan the braking forces acting on the front wheels. Accordingly, the sumof the braking forces acting on the respective left wheels 2, 46 and thesum of the braking forces acting on the respective right wheels 4, 48are generally equal to each other.(F _(FL))≈(F _(FR) +F _(RR))

Meanwhile, since the arm rR is longer than the arm rL (rR>rL), the yawmoment y is a positive value (y>0) in the present embodiment. Thus, asillustrated in FIG. 14( b), a yaw moment in a right-turning directionacts on the left-hand drive vehicle in the event of the abnormality inthe control system. The yaw moment acting on the vehicle in the event ofthe abnormality in the control system has a direction that causes thevehicle to deviate from an opposite lane in a region where legalregulations stipulate that a left-hand drive vehicle must run on theright side of the road. As a result, for example, when the driverperforms a correcting operation, safety of the vehicle can be improvedwhen compared with a case where a yaw moment having a direction thatcauses the vehicle to move toward the opposite lane acts on the vehicle.In the present embodiment, the power hydraulic pressure source 64, thepressurization linear control valve 172, the common passage 94, theindividual passages 150, the pressure holding valves 153, the brakecylinders 42, 52, and so on are one example of the power hydraulicsystem. Also, the master cylinder 62, the mechanical pressurizationdevice 96, the common passage 94, the individual passages 150FL, RR, thenormally-open pressure holding valves 153FL3, RR3, the master passage76, a normally-open master cut-off valve 194FL3, the brake cylinders42FL, FR, 52RR, and so on are one example of a manual hydraulic system.This manual hydraulic system includes a mixed-type hydraulic pressuredistributor.

It is noted that the same effects can be obtained in a case where aleft-hand drive vehicle includes a brake circuit illustrated in FIG. 2.

<Embodiment 7>

In a hydraulic brake circuit in FIG. 15( a), a master cut-off valve194FL4 corresponding to the brake cylinder 42FL provided for the frontleft wheel 2 is a normally open valve, and a pressure holding valve153FL4 is a normally closed valve. Also, a pressure holding valve 153RL4corresponding to the rear left wheel 46 is a normally open valve, and apressure reduction valve 156RL4 is a normally closed valve. In the eventof an abnormality in the control system, the master pressure is suppliedto the brake cylinder 42FL provided for the front left wheel 2, and theservo pressure in the mechanical pressurization device 96 is supplied tothe brake cylinders 42FR, 52RL provided respectively for diagonal wheels(i.e., the front right wheel 4 and the rear left wheel 46).

A right-turning directional yaw moment y acting on a vehicle that has adriver's seat in its right portion in the forward direction (i.e., avehicle having a steering wheel 300 in its right portion) is representedby the following equation:y=rR(F _(FR))−rL(F _(FL) +F _(RL))In this equation, the sum of the braking forces acting on the respectiveleft wheels 2, 46 and the sum of the braking forces acting on therespective right wheels 4, 48 are generally equal to each other.(F _(FR))≈(F _(FL) +F _(RL))

Meanwhile, since the arm rL is longer than the arm rR (rL>rR), the yawmoment y is a negative value (y<0) and accordingly is a yaw moment inthe left-turning direction as illustrated in FIG. 15( b).

This yaw moment has a direction that causes the vehicle to deviate froman opposite lane in a region where legal regulations stipulate that aright-hand drive vehicle must run on the left side of the road. Thisconfiguration can improve safety of the vehicle in the event of theabnormality in the control system.

In the present embodiment, the master cylinder 62, the mechanicalpressurization device 96, the common passage 94, the individual passages150FR, RL, the normally-open pressure holding valves 153FR4, RL4, themaster passage 76, a normally-open master cut-off valve 194FR4, thebrake cylinders 42FL, FR, 52RL, and so on are one example of a manualhydraulic system. This manual hydraulic system includes a single-typehydraulic-pressure distributor.

<Embodiment 8>

The hydraulic brake system may include a brake circuit illustrated inFIG. 16. The other configurations are the same as those in embodiment 1.In the hydraulic brake circuit illustrated in FIG. 16, the pressurechamber 72 of the master cylinder 62 is coupled to the mechanicalpressurization device 96 by a mechanical-valve input passage 310. Also,since the bypass passage 136 is provided in the mechanicalpressurization device 96, the pressure chamber 72 is coupled to thebrake cylinders 42FL, FR via the mechanical-valve input passage 310, thebypass passage 136, the servo-pressure passage 190, the common passage94, and the individual passages 150FL, 150FR. Thus, the mechanical-valveinput passage 310, the bypass passage 136, the servo-pressure passage190, the common passage 94, the individual passages 150FL, FR, and so oncan be considered to constitute a master passage (not bypassing themechanical pressurization device 96 and can be referred to as anindirect manual passage 311).

Also, a high-pressure cut-off valve 312 is provided in a high-pressurepassage 132 formed between the mechanical pressurization device 96 andthe power hydraulic pressure source 64, and the high-pressure cut-offvalve 312 is in series with the high-pressure-side check valve 100.While the high-pressure cut-off valve 312 is provided nearer to thepower hydraulic pressure source 64 than the high-pressure-side checkvalve 100 in the present embodiment, the high-pressure cut-off valve 312may be provided at any position. The high-pressure-side check valve 100functions in an open state of the high-pressure cut-off valve 312. Thehigh-pressure-side check valve 100 inhibits a flow of the working fluidfrom the mechanical pressurization device 96 to the power hydraulicpressure source 64 and, when the hydraulic pressure produced by thepower hydraulic pressure source 64 is higher than the hydraulic pressurein the mechanical pressurization device 96, a flow of the working fluidfrom the power hydraulic pressure source 64 to the mechanicalpressurization device 96 is allowed. However, the high-pressure-sidecheck valve 100 does not function in a closed state of the high-pressurecut-off valve 312. The inflow and outflow of the working fluid to andfrom the high pressure chamber 114 are inhibited, so that the operationof the mechanical pressurization device 96 is also inhibited.

Also, as in embodiment 1, the input-side cut-off valve 148 is providedin a portion of the mechanical-valve input passage 310. Since theinput-side cut-off valve 148, when being in its closed state, inhibitsthe flow of the working fluid from the master cylinder 62 to the brakecylinders, the input-side cut-off valve 148 can be considered tocorrespond to a master cut-off valve. The input-side cut-off valve 148is provided in the indirect manual passage and is a normally open valve.Also, a pressure-reduction linear control valve 316 is provided betweenthe common passage 94 and the reservoir 78 in the present embodiment.The pressure-reduction linear control valve 316 has generally the samestructure as that of the pressurization linear control valve 172illustrated in FIG. 3. In the pressure-reduction linear control valve316, a pressure differential force related to a pressure differentialbetween the hydraulic pressure in the common passage 94 and thehydraulic pressure in the reservoir 78 acts in a direction in which thevalve element 180 is moved off the valve seat 182. Continuous controlfor a current supplied to the solenoid 186 allows the control for themagnitude of the hydraulic pressure in the common passage 94. It isnoted that the pressure-reduction linear control valve 316 is notessential, and as in embodiment 1, the hydraulic pressure in the commonpassage 94 can be reduced using the pressure reduction valves 156 in theopen states of the pressure holding valves 153.

Furthermore, a separate valve 320 is provided in the common passage 94at a position between a position where the common passage 94 isconnected to the servo-pressure passage 190 and a position where thecommon passage 94 is connected to an individual passage 150RR. Theseparate valve 320 is a normally-closed electromagnetic open/closevalve. In other words, the mechanical pressurization device 96 isconnected to the common passage 94 on a side of the separate valve 320which is nearer to the brake cylinders 42FL, FR provided respectivelyfor the front wheels 2, 4. Also, each of pressure holding valves 153RLa,RRa provided respectively corresponding to the brake cylinders 52RL, RRprovided for the respective rear left and right wheels 46, 48 is anormally open valve.

It is noted that the separate valve 320 is not essential. Also, each ofthe pressure holding valves 153RLa, RRa may be a normally closed valve.

In the present embodiment, the output-side cut-off valve 192 is notprovided. The closed state of the high-pressure cut-off valve 312 makesit difficult for the mechanical movable unit 98 to be operated. Also, inthe closed state of the input-side cut-off valve 148, the hydraulicpressure in the master cylinder 62 is never supplied to thelarger-diameter-side chamber 110, so that the hydraulic pressure in themaster cylinder 62 never moves the stepped piston 104 forward. Thus,establishment of the closed state of the high-pressure cut-off valve 312and the closed state of the input-side cut-off valve 148 achievesgenerally the same effects as obtained in the case where the output-sidecut-off valve is placed in the closed state. Thus, there is a small needto provide the output-side cut-off valve on an output-side of themechanical pressurization device 96. Also, the master passage 74 (i.e.,a direct master passage) is not connected to the pressure chamber 72.This is because a master passage 311 (i.e., an indirect master passage)is provided to lower a need to provide the master passage 74 in additionto the master passage 311. Furthermore, a master-cylinder-pressuresensor 222FR is provided on the master passage 76. Since twomaster-cylinder-pressure sensors are provided, even if there is anabnormality in one of these master-cylinder-pressure sensors, the othermaster-cylinder-pressure sensor can detect the master cylinder pressure.

<Operations in Hydraulic Braking Device>

1) In a Case where System Works Normally

As illustrated in FIG. 17, the input-side cut-off valve 148 is placed inthe closed state, the simulator control valve 202 in the open state, andthe high-pressure cut-off valve 312 in the closed state. Also, thepressure reduction valves 156RL, RR for the respective rear left andright wheels 46, 48 are placed in the closed states, and the separatevalve 320 in the open state. The brake cylinder 42FR is decoupled fromthe master cylinder 62, and the mechanical pressurization device 96 isinhibited to be operated. In this state, the output hydraulic pressureproduced by the power hydraulic pressure source 64 is utilized to supplythe hydraulic pressure in the common passage 94 to the brake cylinders42, 52 under the control of the pressurization linear control valve 172and the pressure-reduction linear control valve 316. The common passage94 and the smaller-diameter-side chamber 112 of the mechanicalpressurization device 96 are in communication with each other, but sincethe input-side cut-off valve 148 is in the closed state, the hydraulicpressure in the smaller-diameter-side chamber 112 is never transferredback to the mechanical-valve input passage 310. Also, since thehigh-pressure cut-off valve 312 is in the closed state, the hydraulicpressure in the accumulator 66 is never supplied to the high pressurechamber 114, so that the hydraulic pressure in the smaller-diameter-sidechamber 112 is maintained. As will be described below, the hydraulicpressure in the smaller-diameter-side chamber 112 is supplied to thelarger-diameter-side chamber 110 via the intra-piston check valve 130,causing the stepped piston 104 to be moved forward and brought intocontact with the valve opening member 125 to close the intra-pistoncommunication passage 129. Also, since the input-side cut-off valve 148is in the closed state, the backward movement of the stepped piston 104is inhibited in principle. Thus, it is considered that this hardlyaffect the control of the hydraulic pressure in the common passage 94.

In the present embodiment, since the pressure holding valves 153RLa, RRaare the normally open valves, the need to supply the current to thesolenoids in normal brake operation is eliminated, whereby powerconsumption can be reduced accordingly.

2) In Case of Abnormality in Control System

As illustrated in FIGS. 18 and 19, no current is supplied to all thesolenoids, so that all the valves are placed back in their respectiveoriginal positions.

2-1) In a Case where Hydraulic Pressure in Larger-Diameter-Side Chamber110 is Equal to or Lower than Actuating Pressure of Mechanical MovableUnit 98

As illustrated in FIG. 18, when the hydraulic pressure in thelarger-diameter-side chamber 110 is equal to or lower than the actuatingpressure of the mechanical movable unit 98, the hydraulic pressure inthe pressure chamber 72 is supplied to the common passage 94 via themechanical-valve input passage 310, the bypass passage 136, and theservo-pressure passage 190 and then to the brake cylinders 42 providedfor the respective front left and right wheels 2, 4. Since the valveopening pressure of the input-side check valve 99 is considerably low,the working fluid can be speedily supplied to the brake cylinders 42 inresponse to the operation for the brake pedal 60, resulting in shortenedbrake response time of each hydraulic brake 40. The brake cylinders42FL, FR provided for the respective front left and right wheels 2, 4are operated as described above in the event of the abnormality in thecontrol system. Thus, in the case where the center of gravity of thevehicle is located at generally the center of the vehicle in the rightand left direction, the generation of the yaw moment can be suppressed.

2-2) In a Case where Hydraulic Pressure in Pressure Chamber 72 is Higherthan Actuating Pressure of Mechanical Movable Unit 98

2-2-1) In a Case where Hydraulic Pressure of Working Fluid Accumulatedin Accumulator 66 is Higher than Actuation Allowing Pressure

In a case where the hydraulic pressure of the working fluid accumulatedin the accumulator 66 is higher than the actuation allowing pressure,even where the operation of the pump device 65 is stopped, themechanical movable unit 98 is allowed to be operated. As illustrated bysolid lines in FIG. 19, the stepped piston 104 is moved forward by thehydraulic pressure in the larger-diameter-side chamber 110 to be broughtinto contact with the valve opening member 125, thereby switching thehigh-pressure supply valve 116 to the open state. Thesmaller-diameter-side chamber 112 is decoupled from thelarger-diameter-side chamber 110, and the high-pressure working fluid issupplied from the accumulator 66 to the high pressure chamber 114 viathe high-pressure-side check valve 100. The hydraulic pressure in thesmaller-diameter-side chamber 112 (i.e., the servo pressure) is madehigher than the hydraulic pressure in the master cylinder 62 andsupplied to the common passage 94 and then to the brake cylinders 42FL,42FR provided for the respective front left and right wheels 2, 4. Themagnitude of the hydraulic pressure in the smaller-diameter-side chamber112 is determined by the hydraulic pressure in the larger-diameter-sidechamber 110 and the ratio between the respective pressure receivingareas of the large diameter portion and the small diameter portion ofthe stepped piston 104.

2-2-2) In a Case where Hydraulic Pressure of Working Fluid Accumulatedin Accumulator 66 is Equal to or Lower than Actuation Allowing Pressure

In a case where the hydraulic pressure of the working fluid accumulatedin the accumulator 66 is equal to or lower than the set pressure, as inthe state illustrated in FIG. 18, the hydraulic pressure in the pressurechamber 72 of the master cylinder 62 is supplied to the brake cylinders42 provided for the respective front left and right wheels 2, 4 via themechanical-valve input passage 310, the bypass passage 136, theservo-pressure passage 190, and the common passage 94. Meanwhile, thehydraulic pressure of the working fluid accumulated in the accumulator66 is higher than the actuation allowing pressure at the actuation ofthe hydraulic brakes 40, but when the hydraulic pressure of the workingfluid accumulated in the accumulator 66 is reduced by the operation ofthe mechanical movable unit 98 and becomes lower than the actuationallowing pressure, the supply of the working fluid from the accumulator66 to the high pressure chamber 114 is stopped. This inhibits themechanical movable unit 98 from being operated or actuated. For example,when the brake is pumped, more working fluid accumulated in theaccumulator 66 is consumed, which may result in the lower accumulatorpressure. The forward movement of the stepped piston 104 is inhibited(it is considered that the stepped piston 104 is brought into contactwith the stopper), so that the hydraulic pressure in thesmaller-diameter-side chamber 112 is not built up any higher, that is,the mechanical movable unit 98 is made unable to exhibit the boostingfunction. The hydraulic pressure in the pressure chamber 72 becomeshigher than the hydraulic pressure in the smaller-diameter-side chamber112, and as indicated by a broken line in FIG. 19, the hydraulicpressure in the pressure chamber 72 of the master cylinder 62 issupplied to the common passage 94 via the bypass passage 136 and theservo-pressure passage 190. The hydraulic pressure in the pressurechamber 72 of the master cylinder 62 is supplied to the brake cylinders42FL, 42FR provided for the respective front left and right wheels 2, 4,without being boosted.

Also, since the separate valve 320 is in the closed state, the hydraulicpressure in the mechanical movable unit 98 is inhibited from beingsupplied to the brake cylinders 52RL, 52RR provided for the respectiverear left and right wheels 46, 48. This reduces the possibility of thefluid shortage and the shortage of the pressure buildup for the brakecylinders 42FL, FR provided for the respective front left and rightwheels 2, 4. Moreover, the volume of the pressure chamber 72 can beincreased in the master cylinder 62. Where the volume of the pressurechamber 72 is increased, even when the working fluid is supplied to bothof the brake cylinders 42FL, FR provided for the respective front leftand right wheels 2, 4, the fluid shortage can be avoided. In this case,the stroke of the brake pedal 60 operated by the driver may be larger.

3) In Case of Possible Leakage

As illustrated in FIG. 20, the input-side cut-off valve 148 is placed inthe open state, the high-pressure cut-off valve 312 in the closed state,and the master cut-off valve 194FR in the open state. Also, the pressurereduction valves 156RL, RR for the respective rear left and right wheels46, 48 are placed in the closed states. Also, the separate valve 320 isplaced in the closed state, and the pressure holding valve 153FR for thefront right wheel 4 in the closed state.

(a) The brake cylinders 52 provided for the respective rear left andright wheels 46, 48 are isolated from the brake cylinders 42 providedfor the respective front left and right wheels 2, 4. In this state, thehydraulic pressure produced by the power hydraulic pressure source 64 iscontrolled by the pressurization linear control valve 172 and thepressure-reduction linear control valve 316 and supplied to the brakecylinders 52 provided for the respective rear left and right wheels 46,48.

(b) The brake cylinder 42FR provided for the front right wheel 4 isisolated from the brake cylinders 42FL, 52RL, RR for the respectivethree wheels. In this state, the hydraulic pressure in the pressurechamber 70 of the master cylinder 62 is supplied to the brake cylinder42FR provided for the front right wheel 4.

(c) The brake cylinder 42FL provided for the front left wheel 2 isisolated from the brake cylinders 52RL, RR provided for the respectiverear left and right wheels 46, 48 and the brake cylinder 42FR providedfor the front right wheel 4. In this state, the hydraulic pressure inthe pressure chamber 72 is supplied to the brake cylinder 42FL providedfor the front left wheel 2 via the mechanical pressurization device 96(the bypass passage 136).

In this case, since the high-pressure cut-off valve 312 is in the closedstate, the operation of the mechanical movable unit 98 is inhibited evenin the open state of the input-side cut-off valve 148. Thus, the equalhydraulic pressure is supplied to the brake cylinders 42FL, FR providedfor the respective front left and right wheels 2, 4.

Also, since the high-pressure cut-off valve 312 is in the closed state,the hydraulic pressure produced by the power hydraulic pressure source64 is not supplied to the mechanical pressurization device 96, so thatthe three brake lines 330FL, FR, R can be independent of one another. Ifthe high-pressure cut-off valve 312 is in the open state (for example,the high-pressure cut-off valve 312 is not provided), the hydraulicpressure produced by the power hydraulic pressure source 64 is suppliedto the brake line 330R including the brake cylinders 52 provided for therespective rear left and right wheels 46, 48 and to the brake line 330FLincluding the brake cylinder 42FL provided for the front left wheel 2,so that these brake lines 330R, 330FL cannot be independent of eachother. Thus, in the event of fluid leakage in the brake line 330FL, thehydraulic pressure produced by the power hydraulic pressure source 64 isconsumed in the brake line 330FL, which may affect the brake line 330R.In contrast, in the case where the high-pressure cut-off valve 312 isplaced in the closed state, it is possible to inhibit an outflow of theworking fluid from the power hydraulic pressure source 64 via themechanical pressurization device 96 even in the event of the fluidleakage in the brake line 330FL.

That is, the establishment of the closed states of the high-pressurecut-off valve 312 and the separate valve 320 can make the three brakelines 330FL, FR, R independent of one another. Thus, even in the eventof fluid leakage in one of these three brake lines, this fluid leakagedoes not affect the other brake lines. The brake line 330FR includes thebrake cylinder 42FR, the master passage 76, the pressure chamber 70, andthe fluid chamber 80. The brake line 330FL includes the brake cylinder42FL, the individual passage 150FL, the common passage 94, theservo-pressure passage 190, the mechanical pressurization device 96, themechanical-valve input passage 310, the pressure chamber 72, and thefluid chamber 82. The brake line 330R includes the brake cylinders 52RL,RR, the individual passages 150RL, RR, the power hydraulic pressuresource 64, and the fluid chamber 84. Accordingly, the state in which thebrake lines 330FR, FL, R are independent of one another means that thefluid chambers 80, 82, 84 of the master reservoir 78 are alsoindependent of one another.

Also, in a case where there is an abnormality in the control system (forexample, the pump device 65 is inoperative, but the control for theelectromagnetic open/close valve is possible), and the hydraulicpressure in the accumulator 66 is lower than the actuation allowingpressure, it is sometimes more effective to switch to the state in FIG.20 than to switch to the state in FIG. 18. In the state in which theoperation of the mechanical movable unit 98 is inhibited, the hydraulicpressure in the pressure chamber 72 is supplied to the brake cylinders42FL, FR provided respectively for the front left and right wheels inthe state in FIG. 18, but the pressure chambers 72, 70 are fluidicallycoupled with the respective brake cylinders 42FL, FR provided for therespective front left and right wheels 2, 4 in the state in FIG. 20,resulting in less shortages of the working fluid in the brake cylinders42FL, FR.

4) In a Case of Release of Hydraulic Brake

Upon release of the braking operation, no current is supplied to thesolenoids of all the valves, so that all the valves are placed back inthe original positions in FIG. 16. Also, in the mechanicalpressurization device 96, the stepped piston 104 is spaced apart fromthe valve opening member 125. The hydraulic pressures in the brakecylinders 42FL, FR provided for the respective front left and rightwheels 2, 4 are returned to the master cylinder 62 (i.e., the masterreservoir 78) via the intra-piston communication passage 129 and theintra-piston check valve 130. Also, the hydraulic pressures in the brakecylinders 52RL, RR provided for the respective rear left and rightwheels 46, 48 are returned to the reservoir 78 via the respectivepressure reduction valves 156.

5) OFF State of Ignition Switch 234

No current is supplied to the solenoids of all the electromagneticopen/close valves, so that all the valves are placed back in theoriginal positions in FIG. 16. Since the three brake lines 330FR, FL, Rare independent of one another as in the case in embodiment 1, even inthe event of fluid leakage in one of these three brake lines, this fluidleakage does not affect the other brake lines. Also, since the outflowpreventing device is provided in the mechanical pressurization device96, the outflow of the working fluid from the master reservoir 78 viathe mechanical pressurization device 96 can be inhibited.

6) Check of Mechanical Pressurization Device 96

In the present embodiment, when predefined check conditions aresatisfied, a check of whether the operation of the mechanicalpressurization device 96 is normal or not is executed.

A check program represented by a flow chart in FIG. 21 is executed ineach predefined set length of time. At S11, it is determined whether thecheck conditions are satisfied or not. When the check conditions are notsatisfied, the check is not executed, but when the check conditions aresatisfied, the check of the operation of the mechanical pressurizationdevice 96 is executed at S12. In the present embodiment, the checkconditions are considered to be satisfied when (i) a first brakeactuating operation is performed for the brake pedal 60 after theignition switch 234 is switched from the OFF state to the ON state, and(ii) the vehicle is in a stopped state. The vehicle can be considered tobe in the stopped state when the running speed of the vehicle which isobtained on the basis of the detection values of the wheel speed sensors230 is equal to or lower than a set speed which can consider that thevehicle is in the stopped state.

The check is thus executed in the operating state of the brake pedal 60.Also, the check is preferably executed in the stopped state of thevehicle but may not be executed in the stopped state. The check includestwo methods: check 1 and check 2. The checks 1 and 2 may be executedsuch that one of the checks 1 and 2 is selectively executed, such thatboth of the checks 1 and 2 are executed when the check conditions aresatisfied, or such that the check 1 is executed when the master-cylinderhydraulic pressure is equal to or higher than a set pressure, and thecheck 2 is executed when the master-cylinder hydraulic pressure is lowerthan the set pressure. As will be described below, the set pressure ofthe master-cylinder hydraulic pressure can be determined to have such amagnitude that allows reliable determination of whether the operation ofthe mechanical pressurization device 96 is normal or not in the check 1.This set pressure may be referred to as “checkable pressure”.

6-1) Check 1

In the check 1, the input hydraulic pressure Pin (Pm) in the mechanicalmovable unit 98 and the output hydraulic pressure Pout (Pwc) in themechanical movable unit 98 are compared with each other to determinewhether the operation of the mechanical pressurization device 96 isnormal or not. As illustrated in FIG. 22( a), the pressurization linearcontrol valve 172 and the pressure-reduction linear control valve 316are placed in the closed states, and the input-side cut-off valve 148and the high-pressure cut-off valve 312 are placed in the open states.In these states, the operation of the mechanical pressurization device96 is allowed. A value Pm detected by a master-cylinder-pressure sensor222FL (i.e., the input hydraulic pressure Pin in the mechanical movableunit 98) and a value Pw detected by the brake-cylinder-pressure sensor226 (i.e., the output hydraulic pressure Pout in the mechanical movableunit 98) are compared with each other. When these values fall within anormal region R illustrated in FIG. 22( b), it can be determined thatthe operation of the mechanical pressurization device 96 is normal. Onthe other hand, when these values do not fall within the normal regionR, it is determined that the operation of the mechanical pressurizationdevice 96 is abnormal. The solid line in FIG. 22( b) represents arelationship between Pin and Pout in the case where the operation of themechanical pressurization device 96 is normal.

The abnormality of the operation of the mechanical pressurization device96 is considered to be caused by at least one of (a) an abnormality inthe power hydraulic pressure source 64 (e.g., a case where the outputhydraulic pressure produced by the power hydraulic pressure source 64 islow and a case where no high hydraulic pressure is supplied from thepower hydraulic pressure source 64, and these cases are considered to becaused by, for example, the fluid leakage from the accumulator 66, afailure of the pump motor 92, the fluid leakage from the high-pressurepassage 132), (b) a stuck-closed fault of the high-pressure cut-offvalve 312, (c) a failure in the mechanical pressurization device 96(i.e., a case where the mechanical movable unit 98 is inoperative, whichis caused by, for example, a stuck-closed fault of the high-pressuresupply valve 116 and an inoperative failure of the stepped piston 104such as seizing up thereof), (d) a stuck-closed fault of the input-sidecut-off valve 148, and other similar causes. Examples of other causesinclude a fault in the master-cylinder-pressure sensor 222FL and/or thebrake-cylinder-pressure sensor 226, a stuck-closed fault of the separatevalve 320, and fluid leakage. In contrast, in the case where theoperation of the mechanical pressurization device 96 is normal, it isconsidered that the operation of the mechanical movable unit 98 isnormal, the high-pressure working fluid is supplied from the powerhydraulic pressure source 64, and the high-pressure cut-off valve 312and the input-side cut-off valve 148 are switched to the open states ascommanded. In other words, in the case where the operation of themechanical pressurization device 96 is normal, it can be determined thatnot only the mechanical pressurization device 96 but also components,devices, and so on associated with the operation of the mechanicalpressurization device 96 are normal.

It is noted that, while the detection value of themaster-cylinder-pressure sensor 222FL is used as the input hydraulicpressure Pin, the detection value of the master-cylinder-pressure sensor222FR or a value estimated based on the detection value of the strokesensors 220 may be used, for example.

Also, in a case where it has already found that at least one of (a) thepower hydraulic pressure source 64, (b) the high-pressure cut-off valve312, (c) the mechanical pressurization device 96, and (d) the input-sidecut-off valve 148 is normal, or more specifically in a case where it hasalready found that these devices are normal, when it is determined thatthe operation of the mechanical pressurization device 96 is abnormal, acause of this abnormality may be obtained.

6-2) Check 2

In the check 2, the stepped piston 104 is moved forward in the closedstate of the mechanical input-side cut-off valve 148 and the closedstate of the high-pressure cut-off valve 312 to build up the hydraulicpressure in the smaller-diameter-side chamber 112 so as to switch thehigh-pressure supply valve 116 to the open state. It is thereafterdetermined whether the operation of the mechanical pressurization device96 is normal or not on the basis of a change in the hydraulic pressurein the smaller-diameter-side chamber 112 after the high-pressure cut-offvalve 312 is controlled to be switched to the open state.

6-2-1) Pre-Check Control

As illustrated in FIG. 23, the pressurization linear control valve 172and the pressure-reduction linear control valve 316 are controlled inthe closed states of the mechanical input-side cut-off valve 148 and thehigh-pressure cut-off valve 312, so that the hydraulic pressure in thecommon passage 94 is changed to a target hydraulic pressure Pref1. Thetarget hydraulic pressure Pref1 has a magnitude that is higher than theactuating pressure of the stepped piston 104 and that causes thehigh-pressure supply valve 116 to be switched to the open state. Withthe stepped piston 104 located at its back end position, theintra-piston communication passage 129 fluidically couples thesmaller-diameter-side chamber 112 and the larger-diameter-side chamber110 with each other. When the hydraulic pressure is supplied to thesmaller-diameter-side chamber 112, the hydraulic pressure is supplied tothe larger-diameter-side chamber 110 via the intra-piston communicationpassage 129 and the intra-piston check valve 130. When the hydraulicpressure in the larger-diameter-side chamber 110 is lower than theactuating pressure, the intra-piston communication passage 129 is keptin the open state, so that the hydraulic pressure in thelarger-diameter-side chamber 110 is increased along the solid line inFIG. 25( a) with an increase in the hydraulic pressure in thesmaller-diameter-side chamber 112. These hydraulic pressures have equalmagnitude (Pin=Pout).

When the hydraulic pressure in the larger-diameter-side chamber 110thereafter reaches the actuating pressure, the stepped piston 104 ismoved forward. This forward movement should cause the followingoperations: the stepped piston 104 is brought into contact with thevalve opening member 125 to close the intra-piston communication passage129, and the valve opening member 125 is moved forward to switch thehigh-pressure supply valve 116 to the open state. The hydraulic pressurein the smaller-diameter-side chamber 112 becomes higher than thehydraulic pressure in the larger-diameter-side chamber 110, and thehydraulic pressure in the smaller-diameter-side chamber 112 becomes theservo pressure. As indicated by one-dot chain lines in FIG. 25( a), thehydraulic pressure in the larger-diameter-side chamber 110 increaseswith the increase in the hydraulic pressure in the smaller-diameter-sidechamber 112. The hydraulic pressure in the smaller-diameter-side chamber112 (i.e., the detection value of the brake-cylinder-pressure sensor226) is controlled by the pressurization linear control valve 172 so asto be brought closer to the target hydraulic pressure Pref1. After thehydraulic pressure in the smaller-diameter-side chamber 112 reaches thetarget hydraulic pressure Pref1, the hydraulic pressure in thesmaller-diameter-side chamber 112 is reduced principally by the controlfor the pressure-reduction linear control valve 316 so as to be broughtcloser to a target hydraulic pressure Pref1. As illustrated in FIG. 25(a), hysteresis of the mechanical movable unit 98 makes the hydraulicpressure in the smaller-diameter-side chamber 112 and the hydraulicpressure in the larger-diameter-side chamber 110 generally equal to eachother. In the present embodiment, since the hydraulic pressure in thesmaller-diameter-side chamber 112 is reduced after the stepped piston104 is moved forward by the increase in the hydraulic pressure in thesmaller-diameter-side chamber 112, a direction of the change in thehydraulic pressure (i.e., hysteresis) is opposite to that in normalbrake operation.

It is noted that, since the check is executed in a state in which thebrake actuating operation is being performed on the brake pedal 60, thepressure holding valves 153 are in the open states, and the pressurereduction valves 156 in the closed states, so that each of therespective hydraulic pressures in all the brake cylinders 42, 52 is thetarget hydraulic pressure Pref1. In this sense, the target hydraulicpressure Pref1 can be adjusted at a magnitude that is determined by abraking force requested by the driver. In most cases, requirement inwhich the target hydraulic pressure Pref1 is higher than the actuatingpressure is satisfied.

6-2-2) Switch of High-Pressure Cut-Off Valve 312

As illustrated in FIG. 24, the pressurization linear control valve 172and the pressure-reduction linear control valve 316 are then switched tothe closed states to form a closed space around thesmaller-diameter-side chamber 112. The space containing thesmaller-diameter-side chamber 112 and the brake-cylinder-pressure sensor226 is isolated from the reservoir 78 and the power hydraulic pressuresource 64 and also from the master cylinder 62 (noted that the mastercut-off valve 194FR is in the closed state). In this state, a current tobe supplied to the solenoid of the high-pressure cut-off valve 312 iscontrolled so as to switch the high-pressure cut-off valve 312 from theclosed state to the open state (that is, no current is supplied to thesolenoid). When the high-pressure working fluid is supplied from thepower hydraulic pressure source 64 to the smaller-diameter-side chamber112, the hydraulic pressure in the smaller-diameter-side chamber 112 isimmediately built up. In the present embodiment, as illustrated in FIG.25( b), a detection value Pwc of the brake-cylinder-pressure sensor 226should be increased to the hydraulic pressure Pref1 and then increasedalong the one-dot chain line. Thus, when the detection value of thebrake-cylinder-pressure sensor 226 is lower than the hydraulic pressurePref1 after the current to be supplied to the solenoid of thehigh-pressure cut-off valve 312 is controlled so as to switch thehigh-pressure cut-off valve 312 from the closed state to the open state,in other words, when an amount of increase ΔPwc of the detection valuePwc is smaller than a determination threshold value ΔPth (=Pref1−Pref2),it is determined that the operation of the mechanical pressurizationdevice 96 is not normal.

FIG. 26 illustrates a routine in the case where the check 2 is executedat S12.

At S21, the input-side cut-off valve 148 is controlled to be placed inthe closed state, and the high-pressure cut-off valve 312 in the closedstate. At S22, a current to be supplied to the pressurization linearcontrol valve 172 is controlled to build up the hydraulic pressure inthe smaller-diameter-side chamber 112 (the common passage 94 and thebrake cylinders 42, 52). Then at S23, it is determined whether thedetection value Pwc of the brake-cylinder-pressure sensor 226 has beenbrought closer to the target hydraulic pressure Pref1 or not. Until thedetection value Pwc has been brought closer to the target hydraulicpressure Pref1, the processings at S22 and S23 are repeated. When thedetection value Pwc has been brought closer to the target hydraulicpressure Pref1, the pressure-reduction linear control valve 316 ismainly controlled at S24 to reduce the hydraulic pressure in thesmaller-diameter-side chamber 112. At S25, it is determined whether thehydraulic pressure in the smaller-diameter-side chamber 112 has beenbrought closer to generally the target hydraulic pressure Pref2 or not.The control for the pressure-reduction linear control valve 316 iscontinued until the hydraulic pressure in the smaller-diameter-sidechamber 112 has been brought closer to the target hydraulic pressurePref2. Then at S26, the pressurization linear control valve 172 and thepressure-reduction linear control valve 316 are placed in the closedstates, and the high-pressure cut-off valve 312 in the open state toform the closed space. Then at S27, it is determined whether or not thedetection value Pwc of the brake-cylinder-pressure sensor 226 becomesequal to or higher than the hydraulic pressure Pref1. When thebrake-cylinder hydraulic pressure is built up, it is determined at S28that the operation of the mechanical pressurization device 96 is normal.When the brake-cylinder hydraulic pressure is not built up, it isdetermined at S29 that the operation of the mechanical pressurizationdevice 96 is not normal.

In the present embodiment as described above, the check can be executedin the state in which the brake actuating operation is being performedon the brake pedal 60, i.e., in normal braking, resulting in increase inopportunities of the check and improvement in a reliability of thehydraulic brake system.

Also, since the input-side cut-off valve 148 is in the closed state, areaction force applied to the brake pedal 60 does not change due to thecheck, thereby suppressing lowering of operation feeling of the driver.

Also, since the input-side cut-off valve 148 is in the closed state,each target hydraulic pressure Pref may have a magnitude that is notrelated to a state of the braking operation of the driver. In the check1, when the input hydraulic pressure Pm is lower than the checkablepressure, it is impossible to accurately determine whether the operationof the mechanical pressurization device 96 is normal or not. In thecheck 2, on the other hand, since each of the target hydraulic pressuresPref 1, 2 is set at any magnitude (within a range higher than theactuating pressure), it is possible to accurately determine whether theoperation of the mechanical pressurization device 96 is normal or not,thereby improving the reliability of the hydraulic brake system.

It is noted that it is possible to wait until a predefined set length oftime has passed before the processing at S27 is executed. In thisembodiment, the presence or absence of the change in the hydraulicpressure in the smaller-diameter-side chamber 112 can be accuratelydetected.

Also, a magnitude of the target hydraulic pressure Pref1 is not limitedto be a magnitude related to a braking torque requested by the driver.The target hydraulic pressure may have any magnitude as long as thetarget hydraulic pressure is capable of switching the high-pressuresupply valve 116 to the open state.

Also, the check 2 is executable in the non-operated state of the brakepedal 60, in other words, in a case where a parking brake, not shown, isin a working state (or in a case where a shift position is located at aparking position). In this case, all the pressure holding valves 153 maybe in the closed states, and the pressure holding valves 153RL, RRcorresponding to the brake cylinders 52 of the respective rear left andright wheels may be in the closed states. In this embodiment, the closedspace containing the smaller-diameter-side chamber 112 and thebrake-cylinder-pressure sensor 226 can be made narrower, allowing theaccurate detection of the change in the hydraulic pressure in thesmaller-diameter-side chamber 112. Also, there is a low need to set themagnitude of the target hydraulic pressure Pref1 at the magnituderelated to the braking torque requested by the driver.

Also, in the check 2, the processings at S24 and S25 are not essential.The high-pressure cut-off valve 312 may be switched from the closedstate to the open state after the hydraulic pressure in thesmaller-diameter-side chamber 112 has reached the target hydraulicpressure Pref1 (in the case where the positive decision (YES) has beenmade at S23). In this configuration, the hydraulic pressure in thesmaller-diameter-side chamber 112, i.e., the brake-cylinder hydraulicpressure should increase along the one-dot chain line in FIG. 25( c).Thus, it is determined that the operation of the mechanical movable unit98 is normal, in a case where the brake-cylinder hydraulic pressure hasincreased from the hydraulic pressure Pref1 by equal to or higher thanan abnormality-determination threshold value ΔPth after a predefined setlength of time is elapsed after the high-pressure cut-off valve 312 isswitched from the closed state to the open state.

Also, when the detection value Pwc has not reached the target hydraulicpressure Pref1 at S23 within a set length of time or when the hydraulicpressure in the smaller-diameter-side chamber 112 has not reached thetarget hydraulic pressure Pref2 at S25 within a set length of time, itmay be determined that the operation of the mechanical pressurizationdevice 96 is normal.

Also, when the brake-cylinder hydraulic pressure Pwc transientlyincreases after the high-pressure cut-off valve 312 is switched from theclosed state to the open state, it may be determined that the operationof the mechanical pressurization device is normal.

Also, the check may be executed after the ignition switch 234 isswitched from the ON state to the OFF state. In this configuration, amagnitude of the target hydraulic pressure in the smaller-diameter-sidechamber 112 may be any value.

Also, the hydraulic pressure in the smaller-diameter-side chamber 112may be controlled also when the check is executed by a first checker.

Also, the application of the present embodiment is not limited to thehydraulic brake system, and the present embodiment may be widely appliedto a hydraulic-pressure operating system.

In the present embodiment, portions of the brake ECU 56 which store andexecute the check program are one example of a pressurization-devicecheck device. Portions of the pressurization-device check device whichstore and execute the processing at S12 are one example of the firstchecker and a second checker. Each of the first checker and the secondchecker is also an input-hindered-state check executer and an operatingchecker. A portion of the first checker which executes the first checkto determine that the operation of the mechanical pressurization device96 is normal is one example of a first normality determiner. Portions ofthe second checker which store and execute the processings at S27 andS28 and so on are one example of a second normality determiner and aservo-state-transition normality determiner (aservo-state-pressurization normality determiner in a case where theprocessings at S24 and S25 are not executed). Portions of the secondchecker which store and execute the processing at S26 and so on are oneexample of a high-pressure cut-off valve controller. Portions of thesecond checker which store and execute the processings at S22-S26 and soon are one example of a pre-check output-side hydraulic-pressurecontroller. Portions of the pre-check output-side hydraulic-pressurecontroller which store and execute the processings at S22 and S23 and soon are one example of a pressurization controller, and portions of thepre-check output-side hydraulic-pressure controller which store andexecute the processings at S24 and S25 and so on are one example of apressure-reduction controller. Also, portions of the pre-checkoutput-side hydraulic-pressure controller which store and execute theprocessing at S26 and so on are one example of a closed-space former.

<Embodiment 9>

A mechanical/power hydraulic-pressure control device 400 may be usedinstead of the mechanical pressurization device 96. One example of thismechanical/power hydraulic-pressure control device 400 is illustrated inFIGS. 27 and 28. The other configurations are the same as those inembodiment 1.

As illustrated in FIG. 27, the mechanical/power hydraulic-pressurecontrol device 400 is provided among the power hydraulic pressure source64, the master passage 74, and the common passage 94. Themechanical/power hydraulic-pressure control device 400 has a function asthe pressurization device. The mechanical/power hydraulic-pressurecontrol device 400 includes: a mechanical/power movable unit(hereinafter simply referred to as “movable unit”) 410; a bypass passage412 bypassing the mechanical/power movable unit 410 to connect betweenthe master passage 74 and the common passage 94; a check valve 414provided in the bypass passage 412; and a high-pressure-side check valve416 provided between the mechanical/power hydraulic-pressure controldevice 400 and the power hydraulic pressure source 64. Also, aninput-side cut-off valve 420 is provided between the mechanical/powerhydraulic-pressure control device 400 and the master passage 74, and anoutput-side cut-off valve 422 is provided between the mechanical/powerhydraulic-pressure control device 400 and the common passage 94. Asillustrated in FIG. 28, the movable unit 410 is operable by one of anelectromagnetic driving force produced by a solenoid 432 and a hydraulicoperating force corresponding to the master-cylinder hydraulic pressurePm (i.e., a pilot pressure). In the event of the abnormality in theelectrical system, the movable unit 410 is operable by the hydraulicoperating force corresponding to the master-cylinder hydraulic pressurePm. The movable unit 410 is described in JP-A-2010-926, and a detailedexplanation thereof is omitted.

The mechanical/power movable unit 410 includes: (i) a housing 434 havinga stepped cylinder bore; (ii) a master-hydraulic-pressure receiver 436fluid-tightly and slidably fitted in a large-diameter portion of thecylinder bore of the housing 434; (iii) a first valve member 440 engagedwith the master-hydraulic-pressure receiver 436; (iv) a plunger 442slidably fitted in a small-diameter portion of the cylinder bore; and(v) a second valve member 444 engaged with the plunger 442 with a powertransmission member 443 therebetween.

The first valve member 440 has a generally cylindrical shape and has aninner face on which the second valve member 444 is slidably disposed. Ahigh-pressure supply valve 446 is formed by the first valve member 440and the second valve member 444. A portion of the first valve member 440is a valve seat 448, and a portion of the second valve member 444 is avalve element 449. The first valve member 440 and the second valvemember 444 are moved relative to each other to open and close thehigh-pressure supply valve 446. In this sense, the first valve member440 can be referred to as “valve seat member”, and the second valvemember 444 as “valve element member”. Also, the first valve member 440is one example of an outer-circumferential-side member, and the secondvalve member 444 is one example of an inner-circumferential-side valvemember. Also, a reservoir cut-off valve 452 is constituted by theplunger 442 and the power transmission member 443. The powertransmission member 443 has a liquid passage 454 with which an engagingportion 455 of the plunger 442 is engaged, with the engaging portion 455facing an opening portion of the liquid passage 454. The engagingportion 455 of the plunger 442 is brought into contact with andseparated from the opening portion of the liquid passage 454 to open andclose the opening portion of the liquid passage 454. The engagingportion 455 of the plunger 442 is one example of a valve element, and aperiphery of the opening portion of the liquid passage 454 is oneexample of a valve seat.

The housing 434 has a master pressure port 458, an output port 460, ahigh pressure port 462, and two low pressure ports 464, 466. The masterpassage 74 is connected to the master pressure port 458, theservo-pressure passage 190 is connected to the output port 460, thepower hydraulic pressure source 64 is connected to the high pressureport 462, and the master reservoir 78 is connected to the low pressureports 464, 466. The high-pressure supply valve 446 couples and decouplesthe output port 460 and the high pressure port 462 to and from eachother, and the reservoir cut-off valve 452 couples and decouples theoutput port 460 and the low pressure port 466 to and from each other.Opening and closing of the high-pressure supply valve 446 and thereservoir cut-off valve 452 control a hydraulic pressure in the outputport 460.

Also, a spring 470 is provided between the plunger 442 and the housing434 to urge the plunger 442 backward. A spring 472 is provided betweenthe power transmission member 443 and the first valve member 440 to urgethem so as to expand a space therebetween. A spring 476 is providedbetween the first valve member 440 and the second valve member 444 tourge the high-pressure supply valve 446 such that the high-pressuresupply valve 446 is placed in a closed state. As thus described, thehigh-pressure supply valve 446 is a normally closed valve, and thereservoir cut-off valve 452 is a normally open valve.

When a current is supplied to a coil 480, the plunger 442 is movedforward against an urging force of the spring 470 and brought intocontact with the power transmission member 443. As a result, the liquidpassage 454 is closed, and the reservoir cut-off valve 452 is placed ina closed state. The power transmission member 443 is moved upward inFIG. 28 against an urging force of the spring 472, and the second valvemember 444 is moved upward relative to the first valve member 440against an urging force of the spring 476. As a result, thehigh-pressure supply valve 446 is placed in an open state. The outputport 460 is decoupled from the low pressure port 466 and coupled to thehigh pressure port 462, so that the hydraulic pressure in the outputport 460 can be built up. A power control pressure as the hydraulicpressure in the output port 460 is supplied to the common passage 94. Inthe present embodiment, the solenoid 432 is constituted by the coil 480and the plunger 442.

It is noted that the first valve member 440 is located at its back endposition, and the master-hydraulic-pressure receiver 436 is held incontact with a stopper 482, so that an upward movement of themaster-hydraulic-pressure receiver 436 from an illustrated position isinhibited. Thus, the hydraulic pressure in the output port 460 can bebuilt up in a state in which the brake pedal 60 is not operated, so thatthe automatic brake can be actuated.

When the master-cylinder hydraulic pressure Pm is applied, themaster-hydraulic-pressure receiver 436 is moved downward in FIG. 28, sothat the first valve member 440 is moved downward relative to the secondvalve member 444. The power transmission member 443 is pushed on theplunger 442 via the spring 472, so that the liquid passage 454 isclosed. The reservoir cut-off valve 452 is placed in a closed state, andthe high-pressure supply valve 446 in the open state. The output port460 is decoupled from the low pressure port 466 and coupled to the highpressure port 462, so that the hydraulic pressure in the output port 460is built up, and the control pressure is supplied to the common passage94.

An operation in the brake circuit configured as described above will beexplained.

1) In a Case where System Works Normally

In the present embodiment, the regenerative cooperative control isexecuted.

A current to be supplied to the coil 480 is controlled on the basis of acommand output from the brake ECU 56. The pressure holding valves 153for all the four wheels are placed in the open states, the pressurereduction valves 156 for all the four wheels in the closed states, thesimulator control valve 202 in the open state, and the input-sidecut-off valve 420 and the output-side cut-off valve 422 in closedstates. Since the input-side cut-off valve 420 is in the closed state,the master-cylinder hydraulic pressure Pm is never applied to the masterpressure port 458. A total required braking torque is obtained, and avalue obtained by subtracting an actually-applied regenerative brakingtoque from the total required braking torque is determined as a requiredhydraulic braking torque, and a hydraulic pressure corresponding to therequired hydraulic braking torque is determined as a target hydraulicpressure. The current to be supplied to the coil 480 is controlled suchthat the brake-cylinder hydraulic pressure Pwc actually detected by thebrake-cylinder-pressure sensor 226 is brought closer to the targethydraulic pressure Pref. In other words, the current to be supplied tothe coil 480 is controlled such that the hydraulic pressure in theoutput port 460 of the mechanical/power hydraulic-pressure controldevice 400 is brought closer to the target hydraulic pressure Pref. Inthe present embodiment as thus described, the mechanical/powerhydraulic-pressure control device 400 utilizes the output hydraulicpressure produced by the power hydraulic pressure source 64 to controlthe hydraulic pressure in the common passage 94, eliminating a need toprovide the pressurization linear control valve 172 and thepressure-reduction linear control valve 316.

Also, the hydraulic pressure in the output port 460 may be controlled ata magnitude that is lower than the hydraulic pressure in the mastercylinder 62.

2) In Case of Abnormality in Control System

In case where there is an abnormality in the control system, no currentis supplied to the solenoids of the electromagnetic open/close valves,so that the electromagnetic open/close valves are placed back in theoriginal positions illustrated in FIG. 27. In the mechanical/powerhydraulic-pressure control device 400, since no current is supplied tothe coil 480, the plunger 442 is located at its back end position. Uponthe brake actuating operation on the brake pedal 60, a hydraulicpressure related to the operating force of the brake pedal 60 isproduced in the pressure chamber 72 of the master cylinder 62. Thehydraulic pressure in the pressure chamber 72 is supplied to the movableunit 410 via the master pressure port 458 to move themaster-hydraulic-pressure receiver 436 and the first valve member 440relative to the second valve member 444. Also, the power transmissionmember 443 is pressed against the engaging portion 455 of the plunger442. As a result, the reservoir cut-off valve 452 is placed in theclosed state, and the high-pressure supply valve 446 in the open state.

Where the high-pressure working fluid is accumulated in the accumulator66, the hydraulic pressure in the output port 460 is made higher thanthe master hydraulic pressure (the master-cylinder hydraulic pressure)Pm. The hydraulic pressure in the output port 460 is supplied to thebrake cylinders 42FL, FR provided for the respective front left andright wheels 2, 4, via the servo-pressure passage 190 and the commonpassage 94. On the other hand, where no hydraulic pressure is suppliedfrom the accumulator 66, the hydraulic pressure in the master cylinder62 is higher than the hydraulic pressure in the control-pressure port460, so that the hydraulic pressure in the pressure chamber 72 issupplied to the common passage 94 via the bypass passage 412. It isnoted that even where no hydraulic pressure is supplied from theaccumulator 66, the reservoir cut-off valve 452 is placed in the closedstate by the application of the master pressure to the master pressureport 458, so that the control-pressure port 460 is isolated from the lowpressure port 466.

3) In Case of Possible Fluid Leakage

The input-side cut-off valve 420 is placed in the closed state, and thepressure holding valves 153FL, FR for the respective front left andright wheels 2, 4 are placed in the closed states. Also, the pressureholding valves 153RL, RR for the respective rear left and right wheels46, 48 are placed in the open states, and the pressure reduction valves156RL, RR are placed in the closed states. The hydraulic pressurecontrolled by the control of the current to be supplied to the coil 480in the mechanical/power hydraulic-pressure control device 400 issupplied to the brake cylinders 52RL, RR provided for the respectiverear left and right wheels 46, 48. The master hydraulic pressures arerespectively supplied from the pressure chambers 70, 72 of the mastercylinder 62 to the brake cylinders 42FL, FR provided for the respectivefront left and right wheels 2, 4. In view of the above, a brake line490FL including the brake cylinder 42FL provided for the front leftwheel 2, a brake line 490FR including the brake cylinder 42FR providedfor the front right wheel 4, and a brake line 490R including the brakecylinders 52RL, RR provided for the respective rear left and rightwheels 46, 48 are made independent from one another, so that fluidleakage in one of these lines does not affect the other brake lines.

4) In a Case of Release of Hydraulic Brake

The valves are placed back in the original positions illustrated in FIG.27. The hydraulic pressures in the brake cylinders 52RL, RR provided forthe respective rear left and right wheels 46, 48 are returned to themaster reservoir 78 via the respective pressure reduction valves 156RL,RR. The hydraulic pressures in the brake cylinders 42FL, FR provided forthe respective front left and right wheels 2, 4 are returned to themaster reservoir 78 via the reservoir cut-off valve 452 and the lowpressure port 466 of the movable unit 410.

It is noted that the mechanical/power hydraulic-pressure control device400 can control the current to be supplied to the coil 480 in a state inwhich the hydraulic pressure in the master cylinder 62 is applied to themaster pressure port 458. Since the master cylinder pressure is appliedto the power transmission member 443 via the spring 472, the current tobe supplied to the coil 480 can be controlled to control relativepositions of the first valve member 440 and the second valve member 444,so that the hydraulic pressure in the output port 460 can be determinedat a magnitude related to the hydraulic pressure in the master cylinder62.

<Embodiment 10>

The check of the pressurization device can be executed in a hydraulicbrake circuit illustrated in FIGS. 29 and 30. A mechanicalpressurization device illustrated in FIG. 30 is described inJP-A-2001-225739 and will be briefly explained. The other configurationsare the same as those in embodiment 1.

In FIG. 29, a master cylinder 500 includes: a housing 502; twopressurizing pistons 504, 506 slidably fitted in the housing 502;pressure chambers 510, 512 formed in front of the respectivepressurizing pistons 504, 506; and a rear hydraulic-pressure chamber 514formed at a rear of the pressurizing piston 504. The pressurizing piston504 is mechanically coupled with the brake pedal 60. Master passages520, 522 are connected to the respective pressure chambers 510, 512. Themaster passage 520 is connected to the brake cylinders 42 provided forthe respective front left and right wheels 2, 4, and the master passage522 is connected to the brake cylinders 52 provided for the respectiverear left and right wheels 46, 48. A brake-cylinder hydraulic sensor 524is provided in the master passage 520. The hydraulic brake circuit inthe present embodiment has front and rear lines, namely afront-wheel-side line and a rear-wheel-side line. In thefront-wheel-side line, an antilock control device 525 is provided amongthe brake cylinders 42FL, FR, the pressure chamber 510, and a reservoir,not shown. In the rear-wheel-side line, an antilock control device 526is provided among the brake cylinders 52RL, RR, the pressure chamber512, and the reservoir.

A pressurization device 530 and a hydraulic-pressure control device 532are coupled in parallel to the rear hydraulic-pressure chamber 514. Eachof the pressurization device 530 and the hydraulic-pressure controldevice 532 utilizes the hydraulic pressure produced by the powerhydraulic pressure source 64. The hydraulic-pressure control device 532includes a pressurization linear control valve 540 and apressure-reduction linear control valve 542 which are controlled tocontrol the hydraulic pressure produced by the power hydraulic pressuresource 64 such that the controlled hydraulic pressure is supplied to therear hydraulic-pressure chamber 514. The structures of thepressurization linear control valve 540, the pressure-reduction linearcontrol valve 542, and so on are the same as those illustrated in FIG.3.

As illustrated in FIG. 30, the pressurization device 530 includes: astepped piston 552 slidably fitted in a housing 550; and a high-pressuresupply valve 554 provided in front of the stepped piston 552. A space infront of the stepped piston 552 is a smaller-diameter-side chamber 556,and a space at a rear of the stepped piston 552 is alarger-diameter-side chamber 558. The master passage 520 (the pressurechamber 510 of the master cylinder 500) is connected to thelarger-diameter-side chamber 558, and the rear hydraulic-pressurechamber 514 is coupled to the smaller-diameter-side chamber 556. Thehigh-pressure supply valve 554 is provided between thesmaller-diameter-side chamber 556 and a high pressure chamber 559coupled to the power hydraulic pressure source 64. The high-pressuresupply valve 554 includes: a valve seat 560 formed in the housing 550;and a valve element 562 movable relative to the valve seat 560. Thevalve element 562 has a through hole 564 that can fluidically couple thesmaller-diameter-side chamber 556 and a reservoir port 566 with eachother. Provided between the valve element 562 and the housing 550 is aspring 570 that urges the valve element 562 toward the valve seat 560.Provided between the stepped piston 552 and the housing 550 is a spring572 that urges the stepped piston 552 toward its back end position.

With the stepped piston 552 located at the back end position, thehigh-pressure supply valve 554 is in a closed state, so that thesmaller-diameter-side chamber 556 is isolated from the high pressurechamber 559 and coupled to the reservoir port 566. When the steppedpiston 552 is moved forward, the through hole 564 of the valve element562 is closed, and the valve element 562 is moved off the valve seat560, so that the smaller-diameter-side chamber 556 is isolated from thereservoir port 566 and coupled to the high pressure chamber 559 to buildup a hydraulic pressure in the smaller-diameter-side chamber 556. Anoutput-side cut-off valve 574 is provided between the pressurizationdevice 530 and the rear hydraulic-pressure chamber 514. The output-sidecut-off valve 574 is a normally-open electromagnetic open/close valve.

A normally open valve in the form of a pilot cut-off valve 592 isprovided in a pilot passage 590 that connects between thelarger-diameter-side chamber 558 and the master passage 520. A normallyclosed valve in the form of a communication cut-off valve 596 isprovided in a bypass passage (may be referred to as “extra-pistoncommunication passage”) 594 that bypasses the pressurization device 530to couple the smaller-diameter-side chamber 556 and thelarger-diameter-side chamber 558 with each other. A normally closedvalve in the form of a high-pressure cut-off valve 600 is provided in ahigh control pressure passage 598 that couples the accumulator 66 andthe high pressure chamber 559 with each other.

<Check of whether Operation of Pressurization Device 530 is Normal>

In the present embodiment, the check 2 is executed. Also, in the presentembodiment, the check 2 is executed preferably in a state in which thebrake pedal 60 is not being operated. For example, the check 2 can beexecuted when the ignition switch 234 is switched from the ON state tothe OFF state or when the brake pedal 60 is not being operated while thevehicle is in the stopped state.

As illustrated in FIG. 31, the pilot cut-off valve 592 is placed in aclosed state, the communication cut-off valve 596 in an open state, thehigh-pressure cut-off valve 600 in a closed state, and the output-sidecut-off valve 574 in an open state. The pressurization linear controlvalve 540 and the pressure-reduction linear control valve 542 arecontrolled to bring a hydraulic pressure in the rear hydraulic-pressurechamber 514 closer to the target hydraulic pressure Pref.

The hydraulic pressure in the smaller-diameter-side chamber 556 of thepressurization device 530 is made equal to a hydraulic pressure in thelarger-diameter-side chamber 558 of the pressurization device 530, thatis, each hydraulic pressure is made the target hydraulic pressure Pref.When the hydraulic pressure in the larger-diameter-side chamber 558becomes higher than an actuating pressure of the stepped piston 552, thestepped piston 552 should be moved forward and brought into contact withthe valve element 562 of the high-pressure supply valve 554 to close thethrough hole 564. The high-pressure supply valve 554 should be switchedto an open state, and the smaller-diameter-side chamber 556 should beisolated from the reservoir 78. The stepped piston 552 is considered tobe moved forward until the valve element 562 is brought into contactwith a stopper, not shown.

Also, since the output-side cut-off valve 574 is in the open state, anoutflow of the working fluid from the smaller-diameter-side chamber 556is allowed, which allows the forward movement of the stepped piston 552.Also, the hydraulic pressure in the smaller-diameter-side chamber 556 issupplied from the output-side cut-off valve 574 to the rearhydraulic-pressure chamber 514 to build up the hydraulic pressure in therear hydraulic-pressure chamber 514. As a result, the pressurizingpiston 504 is moved forward to build up a hydraulic pressure in thepressure chamber 510, and the hydraulic pressure in the pressure chamber510 is detected by the brake-cylinder hydraulic sensor 524. Apredetermined relationship is established between the hydraulic pressurein the rear hydraulic-pressure chamber 514 and the hydraulic pressure inthe pressure chamber 510. In the present embodiment, a detection valueof the brake-cylinder hydraulic sensor 524 is controlled such that thehydraulic pressure in the rear hydraulic-pressure chamber 514 is broughtcloser to a value that corresponds to the target hydraulic pressurePref.

In this state, a current to be supplied to a solenoid of thecommunication cut-off valve 596 is controlled such that, as illustratedin FIG. 32, the communication cut-off valve 596 is placed in a closedstate, and the high-pressure cut-off valve 600 in an open state. Thesmaller-diameter-side chamber 556 should be isolated from thelarger-diameter-side chamber 558, so that the high hydraulic pressure issupplied from the power hydraulic pressure source 64 to thesmaller-diameter-side chamber 556. It is detected whether the detectionvalue Pwc of the brake-cylinder hydraulic sensor 524 has increased ornot. When the detection value Pwc of the brake-cylinder hydraulic sensor524 has increased, it is determined that an operation of thepressurization device 530 is normal. The stepped piston 552 isconsidered to be moved by the hydraulic pressure in thesmaller-diameter-side chamber 556 and the hydraulic pressure in thelarger-diameter-side chamber 558, so that the hydraulic pressure in thesmaller-diameter-side chamber 556 becomes a value that is higher thanthe hydraulic pressure in the larger-diameter-side chamber 558 by aratio determined by a shape of the stepped piston 552. As describedabove, the present invention is also applicable to the pressurizationdevice provided upstream of the master cylinder 500.

There will be briefly explained a case where the check 2 is executedaccording to the flow chart illustrated in FIG. 33. At S31, currents tobe supplied to solenoids are controlled such that the high-pressurecut-off valve 600 and the pilot cut-off valve 592 are placed in theclosed states, and the communication cut-off valve 596 in the openstate. At S32 and S33, the pressurization and pressure-reduction linearcontrol valves 540, 542 are controlled to bring the hydraulic pressuredetected by the brake cylinder hydraulic sensor 524 closer to the targethydraulic pressure. At S34, the pressurization and pressure-reductionlinear control valves 540, 542 are placed in the closed state, and thecommunication cut-off valve 596 is switched to the closed state, and thehigh-pressure cut-off valve 600 to the open state. At S35, it isdetermined whether the hydraulic pressure detected by the brake cylinderhydraulic sensor 524 has increased or not. When the hydraulic pressuredetected by the brake cylinder hydraulic sensor 524 has increased, it isdetermined at S36 that the operation of the pressurization device 530 isnormal. When the hydraulic pressure detected by the brake cylinderhydraulic sensor 524 has not increased, it is determined at S37 that theoperation of the pressurization device 530 is not normal.

In the present embodiment, portions of the brake ECU 56 which store andexecute the processing at S32 and S33, and so on are one example of apre-check input-side hydraulic-pressure pressurization controller, andportions of the brake ECU 56 which store and execute the processing atS35-S37, and so on are one example of aninput-hydraulic-pressure-control normality determiner. Also, portions ofthe brake ECU 56 which store and execute the processing at S31 and S34,and so on are one example of a communication-cut-off-valve controller.

<Embodiment 11>

The system may be configured such that in the event of the abnormalityin the control system, the servo pressure is supplied to brake cylindersof respective wheels located at diagonal positions. One example of thisconfiguration is illustrated in FIG. 34.

The master cut-off valve 194FR3 may be replaced with a normally closedvalve (namely a master cut-off valve 194FRb) in the brake circuitillustrated in FIG. 13( a). In the present embodiment, in the event ofthe abnormality in the control system, the servo pressure is supplied tothe brake cylinders 42FL, 52RR provided respectively for the front leftwheel 2 and the rear right wheel 48. As illustrated in FIG. 34( b), inthe vehicle having the steering wheel 302 in its left portion, a brakeforce applied to the right wheels (near the longer arm) is smaller thana brake force applied to the left wheels (near the shorter arm), wherebythe generation of the yaw moment can be suppressed. In the presentembodiment, portions of the brake ECU 56 which store and execute theprocessing at S5, and so on are one example of a secondhydraulic-pressure supplier. Also, the pressure chamber 72 is oneexample of the first manual hydraulic pressure source, and themechanical pressurization device 96 is one example of the second manualhydraulic pressure source.

<Embodiment 12>

Likewise as illustrated in FIG. 35( a), the master cut-off valve 194FL4may be replaced with a normally closed valve (namely a master cut-offvalve 194FLc) in the brake circuit illustrated in FIG. 14( a). In thepresent embodiment, the servo pressure is supplied to the brakecylinders 42FR, 52RL respectively provided for the front right wheel 4and the rear left wheel 46. As illustrated in FIG. 35( b), in thevehicle having the steering wheel 300 in its right portion, a brakeforce applied to the left wheels (near the longer arm) is smaller than abrake force applied to the right wheels (near the shorter arm), wherebythe generation of the yaw moment can be suppressed. In the presentembodiment, portions of the brake ECU 56 which store and execute theprocessing at S5, and so on are one example of the secondhydraulic-pressure supplier. Also, the pressure chamber 72 is oneexample of the first manual hydraulic pressure source, and themechanical pressurization device 96 is one example of the second manualhydraulic pressure source.

While the embodiments have been described above, two or more of theseembodiments are implemented in combination.

It is to be understood that the present invention is not limited to thedetails of the illustrated embodiments, but may be embodied with variouschanges and modifications, which may occur to those skilled in the art,for example, two or more of these embodiments can be implemented incombination.

Description of Reference Numerals

40, 50: hydraulic brake, 42, 52: brake cylinder, 54: hydraulic-pressurecontroller, 56: brake ECU, 60: brake pedal, 62: master cylinder, 64:power hydraulic pressure source, 66: accumulator, 70, 72: pressurechamber, 74, 76: master passage, 94: common passage, 96: mechanicalpressurization device, 98: mechanical movable unit, 99: input-side checkvalve, 100: high-pressure-side check valve, 104: stepped piston, 110:larger-diameter-side chamber, 112: smaller-diameter-side chamber, 116:high-pressure supply valve, 132: high-pressure-side check valve, 136:bypass passage, 148: input-side cut-off valve, 150: individual passage,153: pressure holding valve, 156: pressure reduction valve, 170: powerhydraulic pressure passage, 172: pressurization linear control valve,190: servo-pressure passage, 192: output-side cut-off valve, 218: brakeswitch, 220: stroke sensor, 222: master-cylinder-pressure sensor, 226:brake-cylinder-pressure sensor, 228: level warning, 250FL, FR, R: brakehydraulic line, 260, 270, 280: outflow preventing device, 272, 282:first check valve, 274, 284: second check valve, 300, 302: steeringwheel, 330FL, FR, R: brake hydraulic line, 400: mechanical/powerpressurization device, 410: mechanical/power movable unit, 432:solenoid, 436: master-hydraulic-pressure receiver, 440: first valvemember, 442: plunger, 443: power transmission member, 444: second valvemember, 446: high-pressure supply valve, 452: reservoir cut-off valve,500: master cylinder, 514: rear hydraulic-pressure chamber, 520: masterpassage, 530: pressurization device, 532: hydraulic-pressure controldevice, 574: output-side cut-off valve, 596: communication cut-offvalve, 592: pilot cut-off valve, 594: bypass passage, 600: high-pressurecut-off valve

What is claimed is:
 1. A hydraulic brake system comprising: a pluralityof hydraulic brakes provided respectively for front left, front right,rear left and rear right wheels of a vehicle, and each of the pluralityof hydraulic brakes being configured to operate by a hydraulic pressurein a corresponding one of a plurality of brake cylinders to restrainrotation of a corresponding one of the front left, front right, rearleft and rear right wheels of the vehicle; a power hydraulic pressuresource configured to produce a hydraulic pressure by supply of electricenergy; at least one manual hydraulic pressure source configured toproduce a hydraulic pressure by a braking operation of a driver; apressurization device configured to operate by at least a hydraulicpressure produced by one manual hydraulic pressure source of the atleast one manual hydraulic pressure source, the pressurization devicebeing capable of outputting a hydraulic pressure that is greater thanthe hydraulic pressure produced by the one manual hydraulic pressuresource of the at least one manual hydraulic pressure source; a commonpassage to which the pressurization device and the power hydraulicpressure source are connected and to which the plurality of brakecylinders respectively provided for the front left, front right, rearleft and rear right wheels are connected; a power hydraulic-pressurecontrol device configured to control a hydraulic pressure in the commonpassage by utilizing the hydraulic pressure produced by the powerhydraulic pressure source; and an abnormal-case servo-pressure supplydevice configured to, when the power hydraulic-pressure control devicecannot control the hydraulic pressure in the common passage, supply aservo pressure to brake cylinders provided respectively for at least twowheels comprising front left and front right wheels of the front left,front right, rear left and rear right wheels, wherein the servo pressureis an output hydraulic pressure provided by the pressurization device,wherein: the pressurization device comprises: (i) anouter-circumferential-side cylindrical portion and aninner-circumferential-side cylindrical portion arranged one inside ofthe other, and (ii) a hydraulic-pressure control valve configured tocouple and decouple a control-pressure port connected to the commonpassage and a high pressure port coupled to the power hydraulic pressuresource to and from each other by relative movement of theouter-circumferential-side cylindrical portion and theinner-circumferential-side cylindrical portion in an axial directionthereof, and a first one of the outer-circumferential-side cylindricalportion and the inner-circumferential-side cylindrical portion ismoveable in the axial direction by the hydraulic pressure produced bythe manual hydraulic pressure source, and a second one of theouter-circumferential-side cylindrical portion and theinner-circumferential-side cylindrical portion is moveable in the axialdirection by a motive force produced by a solenoid.
 2. The hydraulicbrake system according to claim 1, wherein the abnormal-caseservo-pressure supply device includes a three-wheel supplier configuredto supply the servo pressure provided by the pressurization device tobrake cylinders provided respectively for three wheels including thefront left and right wheels.
 3. The hydraulic brake system according toclaim 1, further comprising: two manual hydraulic pressure sources eachas the manual hydraulic pressure source; and a manual-hydraulic-pressureand power-control-pressure supplier configured to, when there is apossibility of fluid leakage in the hydraulic brake system, decouple thebrake cylinders provided for the respective front left and right wheelsfrom the common passage, couple the brake cylinders provided for therespective front left and right wheels respectively to the two manualhydraulic pressure sources, and supply a hydraulic pressure controlledby power hydraulic-pressure control device to the brake cylindersprovided for the respective rear left and right wheels.
 4. The hydraulicbrake system according to claim 1, wherein the brake cylindersrespectively provided for the four wheels are connected to the commonpassage respectively via the four individual brake-side passages inwhich at least four individual control valves are respectively provided,and each of the at least four individual control valves respectivelycorresponds to at least two brake cylinders, the at least two brakecylinders including the brake cylinders provided for the respectivefront left and front right wheels, and at least one of the at least fourindividual control valves is a normally open valve.
 5. The hydraulicbrake system according to claim 1, wherein the brake cylindersrespectively provided for the four wheels are connected to the commonpassage respectively via the four individual brake-side passages inwhich at least four individual control valves are respectively provided,and each of the at least four individual control valves respectivelycorresponds to at least two brake cylinders, the at least one brakecylinder provided for at least one of the rear left and rear rightwheels, and at least one of the at least four individual control valvesis a normally closed valve.
 6. The hydraulic brake system according toclaim 1, wherein the pressurization device is connected to the commonpassage via an output-side cut-off valve that is a normally open valve.7. The hydraulic brake system according to claim 1, further comprising ahydraulic-pressure controller configured to, in a normal condition,isolate the pressurization device from the common passage and controlthe hydraulic pressure produced by the power hydraulic pressure sourceto control the hydraulic pressure in the common passage.
 8. Thehydraulic brake system according to claim 1, wherein the power hydraulicpressure source includes: (a) a pump device, and (b) an accumulatorconfigured to store a hydraulic pressure ejected from the pump device.